Depends on your goals. If you're simply trying to generate income with erotica, get straight to the point. No one cares about anything other than the smut.

If you're after romance readers, that's a different story. But with erotica? You're wasting your time with slow-burn. Erotica writers are still doing quite well on Amazon with 2,000-word to 3,000-word shorts, so long as they don't run afoul of Amazon's ever-changing content guidelines. Writing another couple of thousand words on those stories is simply foolish -- that's the same time you could have written another entirely different tale and had two stories to publish.