A quick survey - only really applies to group roleplays. Please approach this from the perspective of being a player in someone else's game. The question's pretty straightforward; feel free to elaborate your reasons below.
I used to, but not anymore. Besides the fact that there are players who just derive their enjoyment from character creation, I dont trust the stability of group rps sometimes. So there's no point unless we're still playing a month later.
Also I tend to detest character sheets. Gm's dont incorporate them and players never take up my offers to play a big part of the main story lol. So I just treat them as a formality and because it's a familiar process.
I do, but more as a way to gauge the room. You can tell quite a bit about the style of RP someone is looking for from their character sheet or description, so it can be helpful in that way. Otherwise I'll just reference them as I need them.
I skim enough to figure out what my character would know on seeing them, and to check if there's a reason our characters might already be acquainted (for example; if I'm playing a former captain in the aerial navy and someone is playing a current captain, I might reach out to discuss if maybe we served together at some point), or make sure our characters aren't going to want to kill each other soon after meeting.
But I like to leave as much as possible to discover in play.
Depends. I want to know the class and abilities. But I don't want spoilers as to what a character is up to. In role-play, I like the story aspects: Character development, exposition, sub plots... hidden subterfuges. I would honestly start getting exited if a player decided his or her sheet was not for my perusal.
I absolutely read them all, with the following exceptions: If the CS is really long, and/or there are a lot of characters in the RP I'll probably just give it a skim. I'd read more detail if that person is going to be important from my POV or if that character and mine need to know something in depth about each other.
Also it very much depends on how they are written. If it's catching my attention as something fun to read, then I'm more likely to read it properly. If it's just a kind of list of things the person did like "he went there. Then he did this. Then his parents died. Then he met a giant snake," for three - four paragraphs then probably going to assume I don't need to know or care about it.
Learning to summarise things on your character sheet, while making your character still look interesting is a skill in itself and quite a useful one to develop.
I feel like I have a kind of mercenary attitude about this, so sorry guys. XD
If I'm GMing, then I absolutely read the profiles very thoroughly. Same if I'm being asked for feedback, critique or checking.
I absolutely read other character sheets if I'm just a player in someone else's roleplay. Since I generally join stuff with combat-focus, I don't want to write up my character to have the same abilities or skills as others. Not to mention, interactions IC between characters is much easier if I already know what the other characters are like.
I usually read the others' character sheets in order to get an idea of how they're like. I personally find it easier to have the general idea beforehand so that I don't get too confused about their behaviors in-game. When I don't read character sheets, I tend to get overwhelmed when new faces start popping up in-game.