The handful of times I have had the opportunity, I have loved it.
You can't maintain solid clit contact without a lot of shaft contact as well,
And licking her cunt cream off the shaft of his cock is fantastic...
while you are focusing on bringing her to orgasm, and your buddy is focusing on thrusting, your hands are free to wrap around the base of his sack and pull his balls way out, while you stimulate his perineum or ass with your other hand.
If he is really fucking with abandon, occasionally he will pull too far out and the next thrust will be into your face, so you keep your mouth open so your jaw won't be in the way and it will slide right into your mouth... you then get to steer him back into her cunt, using nothing but your lips on the shaft, cause, y'know, your hands are busy...
When he cums, his final thrusts will pull out a delicious mix of cunt cream and spooge that slides down into your mouth... and afterward, as he pulls out, you place your tongue so its on his shaft and skim it clean.
Then you get to clean her out to the sound of however many more orgasms she has in her...
if you're kinda orally fixated, its hotter than hell.