Firstly it's usually not about swallowing. It's about finishing. By necessity, you'd need to stop just as everything is coming to a climax and do something else. Hand job for instance. If a guy wanted a hand job, he'd do it himself. He's better than you at it. He's getting a blow job, which is awesome, and having it followed through to completion is amazing.
Secondly, he'd rather you not suddenly pull away in disgust. It's a rejection, which kills the mood quite handily.
For two reasons... One, it REALLY feels good, and two, it is an act of submission on the part of the woman. Even when the woman wants to swallow, it's a willing act of submission.
i don't i like cu mming on her face
I doubt they do it for scientific pursuits...
they dont have to stop that fluid explosion
It would be gross to try to talk to her if she didn't. Who'd want to talk to a chick while her mouth is full of food?
dunno....never got that.