How important is a character biography? In your opinion, I mean. I'm mostly referring to a character's history, but in a broad sense this includes anything in a biography.

I tend to lean towards unimportant, except where it helps a GM determine a character's appropriateness, or just helps a GM in general. For example coming up with ideas specific to that character or deciding whether or not to let them play.

But as for the player themselves, if they're a good enough player I feel bios really aren't as necessary and can even be a little detrimental. Personally, I've found I need to write a more detailed biography when I don't know the character well enough , and in the writing of the bio I can get a better handle on the character. But I've found that in other cases, if I know the character very well, not having a biography allows me more flexibility. If I know how a character is and how they should act/react, it comes too complex of a personality to put down on paper. It's more intuitive, and putting it on paper.

But that's taking the extreme, no bio vs. bio. What about details regarding a character's life? Background? Especially early life? Sure, childhood is important in how a person develops. But I can't help feeling flexibility to be vague or make things up on the spot is better, instead of memorizing and dealing with an entire life you've written out.