As a restaurateur might say, it's an amuse bouche before the main course.
It's how I know I'm getting to him, so it's a great affirmation that I'm doing it right. I love reading all these answers from women who love sex and love giving head. IRL, I have girlfriends who don't particularly enjoy giving bj's, and some who refuse to do it at all, and I feel sorry for them (and their guys!).