I started out writing as a role player (I still RP), but my character sheets aren't very in-depth. I do use them for both RP characters and non-RP characters, often because the characters I use in role playing end up in my stories.
I don't write some huge equivalent of an encyclopedia entry on them, though. It's just the basic details I start with, mostly so I have something I can pull up and look at to keep from changing the characters eyes or switching their weapon with someone else's, for example.
Here's a sample sheet, the basic format I use for all profiles:
Sample Character Sheet [Usually I have the character's name and the title of the WIP here.]
Name:
Race: I write fantasy, so this does come up often.
Age: Just an approximation, makes it easier to keep their personality consistent.
Height: So I know who's looking up or down at other characters.
Build: I don't do weight cause that's silly, I just mention whether they're fit or fat.
Hair: For consistency in edits.
Eyes: Same as above.
Sometimes there will be a miscellaneous category here, like scales/wings/whatever.
Background: Just a quick reference with all the basics and maybe a few interesting details about their culture and personal history that would be hard to find otherwise.
If the character is a warrior or whatever, I'll also list their primary weapons and general combat style. Makes it easier to visualize the battles. Also any interesting items they may own or picked up during the story.
Now, I don't actually need this sheet to do any writing. It's more of a holdover, something I do because that's how I did it when I started. I usually have a good memory for this sort of thing, and I don't actually use sheets for every single character. I guess you could call it a hobby, it's just something I like doing.
~DragonHeart~