glk35 is right on. Girls appreciate it when they can get down to business without getting hair in their teeth. Plus, if you want your girlfriend to shave her pussy, it's a lot easier to say "Hey, I did it for you, so can you do it for me?"
I've seen a couple of porn actors who leave some trimmed stuff on their lower stomach just above the base of the shaft, sort of like the way girl pornstars will leave a trimmed triangle or strip above their pussy. I guess the idea is that if you shave it all off, that makes you look like a little boy, but it looks "manly" to have a little bit of hair. Whatever works.
Also, if you use lube when you masturbate, it makes it much easier to clean up afterward.
Just my two cents.