One more thing, I also believe its a comfort thing.
When a girl gets to know someone, that she comfortable with, the session will just naturally go that much better.
Let me give an example:
Lets say my buddy on this board, Kromrider, decides to take me along next tuesday up to Julies with him. He gets me in, he makes it easy for me. (remember, this is all hypothetical)
We both want to see a girl named Lola, whatever, Name is not important. Hes seen her 6 times, me my first visit.
Being the gentleman he is, he says BMM, since its your first visit, you go for it. So I do, and guess what, I dont believe Id get the same service from that girl that he would, only because shes knows him well and feels that much more comfortable with him.
It works like this with any girl. They may offer every man great service, but they are only human, and when they have that session that is in their comfort zone, they can relax more and Im sure it reflects during the session.
Only my opinion, but I find it to be quite true with alot of girls I see once, or 20 times.
And on the flip side, Im willing to bet alot of hobbyist feel there is a comfort zone they would rather have for each session.
Its nice when you know you can go pee without being worried the girl is going to go through your wallet.
Or you dont have to worry about her telling anyone you have a 2 inch dick and youre embarrassed.(but they are a damn hard working 2 inches.)