Guess I prefer a semi-detailed character sheet. Where appearance, personality, skills background and other essential traits are listed off in detail or a paragraph or two (unless it's something like age, name, etc.). Outside of that there is skills or abilities and a few other traits but those are more adjustable from roleplay to roleplay based on the universe's lore or setting. I don't think I'm a big fan of the whole 'likes', 'dislikes', and 'fears' sections most of the time since it seems to be just a thrown bit of information. If a character really likes, dislikes or fears something to a strong extreme of being notable, it can be blended into skills or personality traits as a passing mention. 
 
I think it is rather helpful especially for those who are roleplaying a lot since it can help keep track of different characters as well as their separate histories and personalities. If you end up 4 or 5 roleplays each without a character sheet, I figure it may become difficult over time to remember different specific background details and some of them may blend together. It gives a general guideline and reminder to refer back to for players, as well for the GM.

In the GM's case it could easily help rope in possible plot points that the characters would be interested in or involve the characters' specific background traits. It easily helps to identify which characters are too strong for the roleplay or simply do not fit in. There's also the nature of a person's writing skill and level, if someone is consistently writing one liners for their character descriptions in personality, background, and so on it's an obvious red flag if that's not the intended roleplay format.