[esperent]

Rejection: an incredibly complex proof can fall for (comparatively) simple reasons. If the AI scans the entire proof and says yep, there's the flaw, page 126 theorem X contradicts <well established known theorem> then a human can verify this without having to understand the whole proof.

This could lead to the proof being rejected entirely, or fixed and strengthened.

Confirmation: if the AI understands it well enough that we're even considering asking it to confirm the proof, then you can do all kinds of things. You can ask it to simplify the entire proof to make it easier for humans to verify. You can ask it questions about parts of the proof you don't understand. You can ask it if there's any interesting corollaries or applications in other fields. Maybe you can even ask it to rewrite the whole thing in LEAN (although, like the author, I know nothing about LEAN and have no idea if this would be useful).