I think that it's okay to enjoy something as smutty for its own sake; that's a part of life. CD Projekt Red aims to make this a mature title about a dark future. Because sex is such a big part of life, it's fine to include it in a brutally honest way, just as we do with violence, extreme psychological states, gore, and the struggle to succeed in a dystopia.
On top of the smuttiness, take that or leave it, I think that portraying all aspects of sexuality reveals something about the characters' experiences. This gives us a better window into the cloying search for satisfaction in the characters' present and redemption from their pasts. Sex can be a powerful experience, and the simple, smutty pleasure can help to buoy someone (e.g. V) against their inner demons, giving them strength in the moment to grow. Sex is also a strong enough desire to dement a person; having sex is, in many ways, a reprieve from wanting sex, which can give someone room to change, too.
If immersion is the goal, censoring a powerful part of the experience works against that. If relating to what is happening with the character is the goal, censoring a powerful experience of theirs works against that.
I think that if the sex doesn't sacrifice any other part of the game, then it can only add, as long as it's optional and fits well into an overall tasteful experience (even if that tastefulness is used to portray something arguably ugly).