Rimming is a full-service blowjob. Because the cock and balls are not the only areas to focus on. The best blowjobs are extended all the way to the ass. The entire area between the balls and the ass is very sensitive, and good cocksuckers should always pay special attention to it. And when they are willing to go this far, rimming is the logical next step.

The asshole itself is really, really sensitive, and licking it feels absolutely amazing. Only the naughtiest cocksuckers will ever go there, and not even all men know how magnificent a tongue in the ass can feel.