Since the reaction of the sex partners upon first glance seems to be a very popular benefit, I would like to add that, from my point of view, I like the reaction (moans, amazed looks, "Wow", "Jesus!", "Damn!") of the guys when they finally find out what it feels like to get deepthroated.
Quite a few of the very well hung guys (straight, bi or gay) that I had the pleasure of treating to one or more of my blowjobs told me that they did not like oral sex very much, because usually the gals or guys who wanted to suck them couldn't do it or did it badly.
So, apart from the fact that the sight of a huge thick cock being unleashed and coming toward me is very exciting for ME, it gives me great pleasure to provide the guy with a stunning experience in return.