Political scientists have noted that, in contrast to the party conventions, the general election debates do not typically have dramaticeffects on voters.
To the extent that the debates are important in terms of persuasion, the format may slightly favor the challenger, about whom the public knows less.General election debates aren’t like primary debates — there are strong partisan loyalties, the vast majority of debate viewers have already made up their minds about who they’re voting for, and few are willing to change their minds because of what happened in one debate. Does all these mean debates never matter? No.
They give the media a chance to hold candidates'feet to the fire.
They give voters a way to see how candidates handle the pressure of a big audience in a prize fight atmosphere.