It's not necessarily easy to draw an objective line between gratuitous and not. Particularly in the case of slasher horror movies; the nudity felt gratuitous, a cheap way to sell tickets that would make up for other production flaws. But such gratuitous nudity became a defining characteristic of that genre, and so in that sense it wasn't actually gratuitous. Modern horror movies seem to be more sexless now, and IMHO feel incomplete because of it. When it becomes apparent that a movie thinks no amount of explicit gore is too much but a nipple would go too far, it breaks my immersion by making me aware that the film was, in some sense, calculated to be inoffensive.