I imagine most people watching the debates are doing so with a "I hope undecided Fred is listening to this...maybe I'll go on Facebook and make sure he hear candidate's X point, then he'll surely realize what a worthless buffoon candidate Y is!"
Here's some of my own guesswork on how this thing is likely to go down and what the results will prove to be.
None of the facts, figures, or arguments really matter that much.
No one really cares too much about those, no one's going into this debate waiting to hear the numbers on tax policies that will cinch the deal, confirm which ideology is best, and explain which candidate is the "Honest Abe" that's going to reunite this country in a utopia.
What will matter is how each candidate makes you feel and what kind of narrative and impression you attach to each candidate. The facts and figures that "fact checkers" will look into...everyone knows those are largely bogus or irrelevant and people only care when the other candidate gets called a liar so that they can go on Facebook and say "see that, undecided Fred! I told you candidate X was full of it!"
So the real story here will be which candidate works against the caricature being created for them by the opposing candidate and sells a vision or narrative of their own candidacy that is compelling enough to lure in undecided voters and inspire their own people to actually show up and vote.
Clinton's strategy will be to try and draw a contrast between herself as a seasoned, worthy veteran of governing and avoid taking shots other than to demean various Trump comments as "unpresidential" or indicative of an unqualified buffoon who's in over his head.
If you were one of the few unfortunates who watched Biden vs Ryan in the 2012 Vice Presidential debate you may remember Biden talking over Ryan, interrupting him, and rolling his eyes at virtually every comment.
It'd be going too far for Hillary to match that performance, but something similar where she treats Trump like a reckless child that needs to be reined in by a strong adult would make a lot of sense.
The worst thing that could happen would be for him to look presidential in direct comparison to her and thus gain credibility with the college educated voters that are avoiding jumping on his wagon.
If she wants to play this aggressively then she'll look to press Trump on any issue where she feels he gave a weak or ignorant answer to a question from the moderator. Marco Rubio did this to some effect in one of the later GOP debates but then it only served to bolster Cruz as Trump's opposition.
The problem she has in this format is that she tends to operate off a script with highly detailed, prepared plans whereas Trump reacts in the moment. So any plan she has for going after him could be derailed if he goes off script in an effective way and then she's left without a prepared response.
The safer plan would be to rely on the media and her supporters to draw a contrast.
Most of the advantages in the debate are Trump's
Here's a list of just a few of the ways in which he's at advantage in this thing.
Advantage 1: A favorable point spread
Polls indicate that most people, outside of those who already expect to vote for Trump, believe that the debate format will favor Clinton. That means that voter's expectations are higher for Clinton and the debate betting line is basically Clinton -5.
To beat Clinton -5, Trump doesn't have to actually win the debate or tie with her, he just needs to play within five points (so to speak) and he'll come out ahead as a result of exceeding expectations.
If he demonstrates a greater command of policy, details, and avoids any particularly boorish moments that make him hard to take seriously then he'll exceed the expectations of many voters. Clinton has spent much of the last few months building a caricature of Trump as a reckless, racist madman who can't be trusted with the nuclear codes. It's been pretty effective but the problem is that it's such a cartoonish caricature that it may not be that hard for him to blow it up by simply acting like a responsible, measured adult for 90 minutes.
Advantage 2: A simpler message
On an issue like national security, Hillary needs to craft explanations for why being welcoming to immigrants is useful in the fight against terrorism, why her interventionist policies abroad actually do work to the advantage of Americans, and why Russia is a pernicious threat who's activities in the old Eastern bloc should be taken very seriously.
None of those positions are obvious at first glance and will have to be explained in simple, convincing fashion for Americans to hop aboard. If you haven't listened to her much, Clinton isn't necessarily a natural communicator so this should be interesting to observe.
Trump's positions contain a great deal more plain, obvious sense and he communicates them at about an 8th grade level. When Trump says something like, "we need extreme vetting to make sure that dangerous people aren't coming into our country!" that just makes a lot of obvious sense and it then falls on Clinton to explain why we wouldn't use extreme vetting to protect the borders or why Trump doesn't have a monopoly on keeping dangerous people out of the country.
When Trump says something like, "why should we be opposed to Russia? We should be working with them around the globe to defeat radical Islamic terror," it then falls on Clinton to explain why it's better to continue to position our country against Russia's foreign policy despite this shared concern for an issue that is much larger concern to Americans at home then who rules Crimea.
Clinton will try to dismiss his policy prescriptions and campaign values as "racist" and "unserious" while outlining her own policies as being more nuanced and intelligent, but this could be tough given how easily he'll communicate whatever sense there is behind his own stances.
Advantage 3: Hillary's health
The health issues that have dogged Clinton's campaign couldn't be worse for her in terms of the overall persuasion battle for the trust of American voters.
While Clinton is trying to paint Donald Trump as a reckless, racist who shouldn't be trusted with the nuclear codes, Trump is trying to paint Hillary Clinton as a corrupt, conniving, and sickly figurehead of an establishment that doesn't actually care for the average joe.
When videos go viral of her coughing uncontrollably, getting dragged into her van after nearly collapsing, or losing control of her eyes while making speeches...it really fleshes out the caricature and serves his purposes extraordinarily well. Either you see her as more corrupt or as unfit to protect the nation, both of which are killers for her election hopes.
Anything that happens during the debate that even hints at a lack of health on the part of Clinton would be pretty devastating. Of course, if she's actually sick and her eyes go crossways or she faints at her podium...all the more so.
The likely outcomes and consequences
There are lots of legitimately undecided voters out there, or voters who haven't committed in one direction or another at least, who are likely to use the debates to cement their leanings. The big question is, which way are these people already leaning and will the debate serve those leanings?
If you're leaning towards Clinton then a moderate execution of her plan to spell out nuanced, presidential sounding positions while avoiding a seizure should probably do the trick unless Trump really amazed. If he makes some stupid comment then she's in great shape.
If you're leaning toward Trump but just can't bring yourself to do it then a debate in which he avoids too many Trumpisms while having a chance to lay out his simple principles might be enough to convince you to fall in line with the GOP. If she coughs and sputters while trying to explain how Trump is the candidate for the ultrarich despite their massive investment into her candidacy then he's probably in great shape.
My guess is that sharing a stage with Clinton and having a chance to outline his message in his own words to an audience that may include people only familiar with the caricature is probably going to work to Trump's advantage.
Whatever happens, the more politically active Facebook users will declare victory for their preferred candidate, as will the political strategists on television.
Ask yourself, "how did this candidate make me feel?" and you'll have a more accurate sense of what the actual results will be from this charade.