I find a long CS fits for a few reasons, to me at least.

-It shows effort was put into creating the character in the first place.
-Honestly, many of the questions are just extended backstory.
-They show (from a gm perspective) if the person making the sheet "gets" it. There's a problem if questions are answered and they don't fit the context. A simpler/shorter CS can make it harder to tell.
-For me, it gets me thinking about the character. I feel a little more attached to a char I've detailed rather than a random NPC or tiny bio char without much fleshing out.

That said, I've had as much as half of some CS's I have made not come into use ever, in any interpretation.

Sometimes I say F the CS and retcon my own writings. *shrug*