Some lengthy questions (I'm thinking of the 29 year old that wonders if she will be forced to accept online dating because of her age.) are obviously trolls.
A lot of the short questions are from different people asking the same things. Presumably, they could search GaG for past entries on how to perform some sex act or other or to find out each genders preference in the opposite. But the reason they ask on GaG in the first place instead of asking the great Google is the desire for interactivity with another human being.
As long as the question is honestly asked, I'm content to keep answering.
Normally, asking repetitive questions (always the same thing) is not allowed... but the question is of course: what is "the same question"? If someone is asking 20 questions in a year on his or her appearance, some of them may come close to repetitive... so sometimes it will be gray zone :-)
It may not be the same person over and over, it could be several different people who didn't search for similar questions before asking. Then again it could be the same person beating it to death to either find a different set of answers or just be an ass because they have nothing better to do.