I find sex scenes slow and hard to write (and damn, do I curse the lack of elegant synonyms for tongues, lips and fingers while I'm doing it), but annoyingly I also find them useful. I find the pace and mood of the sex and the way they treat each other during it to be a great way to illustrate the development of depth in a relationship when I'm writing two men who absolutely will not talk openly about their feelings - and given the fandoms and pairings I go for, that's pretty much all of them! So I end up using sex scenes as convoluted longhand for, 'I care about you more now.'