I've been over this repeatedly.
The format is designed for television ratings and not to inform.
It tells you next to nothing useful.
There is the vague "how do they perform on TV" but that's not super helpful unless you believe surface messaging is more important than policy.
Even with all that, they have a relatively small and temporary effect on polling and sentiment from what anyone can measure, since there is so little of substance.
It's been that way for years. It was better under the League of Women's Voters, but the Presidential Debate Commission was designed to make sure the debates didn't hurt the campaigns.
I'm very glad to see Biden push back on it and try and force the debates into a mould that might provide something useful, even a little bit.