If that's what it tells you, then you're assuming that a person is putting down everything they know. And as someone who reuses and develops and reuses characters, I'd be comfortable jumping into a RP without even a sheet, lol. But like I said, I don't mind writing it down, but I definitely don't think it's necessary for me or any players to RP

And I mean, backstory is important in any RP. Your character never just spawns outta no where... But as long as you know it, I don't see why its important for anyone else to. Save for the GM, of course. And proving competence to the GM is really the only viable reason I see for requiring personality / background.