I've done many RPs without character sheets (in fact most of my RPing has been that way). Granted it is mostly 1x1 but they were pretty wordy and I knew my partner well. I imagine it could work in a group setting as well, it all depended on the comfort of the GM. I don't like making CSs so when I GM I keep them simple, but I do use them because i have players I may not know well and will want to know something about their character's wants and goals. There aren't any rules about it here on the site though, it's the call of the individual GM.