This is something I've always wondered.
I've sucked a few guys in my past and when it comes to climax they always seem to get such a kick out of having their cum swallowed. One guy even wiped a bit off the side of my face and fed it to me with his finger while he was...well...almost giggling.
Some guys make it known to me before I blow them that they want to be swallowed.
And others are shocked when I do it because they've never had it done to them.
But they all seem to get the hugest kick out of it. I would figure that just getting head would be enough...but it's almost as if they do it just to see someone swallow their spunk.