Depending on which poll you believe, somewhere between 6 and 34 percent of registered voters think that the Presidential debates will be at least "quite important" in determining who they vote for. This tells us more about how the phrasing of poll questions influence headlines more than how important these debates area. Suffice it to say that I expect the debates to be totally worthless.
As both camps know all too well, the goal of this election campaign isn't to promote your own candidate. It isn't to provide a referendum on critical issues. It's simply to tear down the other candidate to the point where people will vote for your candidate because they suck less. I predict the debate will follow this exact pattern. The candidates will provide as little of an answer to the actual questions as they can get away with. They'll then move to their prepared "zingers" (which won't zing), half-truths, evasions, and attacks. Both candidates will try to appear "Presidential" by their own definition of that term. Secretary Clinton is trying for an image of a firm, fair, consensus builder. Mr. Trump is looking to show strength and provide simple, decisive answers. Both will fail.
At the end the night, both sides will claim victory and both sides will develop new attack ads and messages based on perceived slips made by their opponent. Fact checkers will weigh in and be largely ignored; like all modern elections, people are "buying on emotion." After a week or so, a consensus of pundits and pollsters will declare one or the other the winner, and we'll get ready to do it all over again.
So if you're looking for confirmation bias, by all means tune in tonight. But personally, I think your time would be better spent researching your local races and not trying to decide who's going to lead this country by a round of "Last Comic Standing."