The personality section I consider to be one of the most important fields of the character sheet. History, abilities and personality, those are the three things that truly make a character. Though, I would never call someone out on not having their character perfectly follow the personality section they have put up.

What's important to me is that when someone reads a character sheet, they get an idea of who this person is. The other sections aren't guaranteed to do that. So simply having a short paragraph telling me how nice or edgy or whatever this character is? It gives the reader an impression of what kind of character the player wants to play. That impression I find to be important to both the GM and to other players.

Then of course they don't need to strictly stick to the personality section. That's their choice. But at the very least, the reader of the character sheet has gotten an impression. Yeah. Character development is a thing.

Edit: That said, if you as the GM feels it is unnecessary to have, you can totally skip it. As the GM, that's your choice, heh.