... I wish I could say I knew what YMMV means but ain't got the slightest clue. Anyway, I think it sucks to fill out an app in general and be rejected for any reason (I don't know anyone who really enjoys doing rejections, though maybe there are some out there). But I'd rather players have some semblance of their characters voice before they step into my world. I understand it may not be fully developed, but again my game has a set running time so I'm figuring it's best to have it when you come instead of counting on it to arise in game. I'm also trusting that requiring that field will have them take a look at the whole "well how well can I actually write this character" thing.
I work with OCs, and I don't know if that really affects this subject in any way, but if it does I'm guessing that it would be in the fact that there's no examples for the player to fall back on with their character.