Generally speaking, vulgar words aren't really a necessity. If anything, we rely on them too much in society, often using them instead of the massive number of words that can replace them.A lack of them works a lot better for certain scenes in fics. In particular, if the scenes involve a lot of sensual romance, then having vulgar words tends to throw off the sensual, tender nature of the scene with its sharp contrast.And let's be honest; "Fuck" isn't sexy. It's suitable to shout by itself, but sharp gasp, drawn-out moans, and the occasional words often never seeking to be answered, but working as more of a verbal depiction of the character's thoughts in the moment… THOSE tend to be so much better, than simply resorting to "Fuck".