Every genre has its conventions and the sex should always be about the characters and the plot. I think it is possible, even in these days of explicit romances, to pen a lesbian romance that does not have a “sex scene” per se – but it must have lust and passion or the reader won’t buy that “love and happy ever after” premise you spent several hundred pages selling.
Whether it’s suds in the shower or yahoo-bucking-bronco sex is determined by the plot and characters. I know what doesn’t work, and I see it time-to-time in thrillers and mysteries mostly, both in novels and on screen. Roger Ebert dubbed it the SOLI: semi-obligatory lyrical interlude. That’s when our hero stops all thought and activity relevant to main story and has some soft-focused encounter with a hot babe during which personal thoughts and warm fuzziness are explored.
After which the encounter, personal thoughts and warm fuzzinesses are never referred to or experienced again except, perhaps, at the very end when the hot babe shows up for some epilogue activity (if she didn’t die after the encounter to provide some kind of cliched motivation for our hero’s blood thirsty destruction of everything in her/his path).
Not that the hero can’t have an SOLI – but it needs to tells something about the hero or in some way further the plot. I always think it demonstrates that the hero is easily distracted from the task at hand but it seems very rare that that was what the author meant.
So make it make sense. If none or Energizer Bunny makes sense, then go for it.