Personally I think the safest option is giving the player the choice even if that is the most work for the dev.
It's really just about how much work it entails. Most games avoid the excess work by putting the decision off until the end, and having the next step be Post-Game Renders, in which case, they only need say, a few per ending.
If I offer you say, 8 girls, in which you can end up with anywhere from 0 to 8 in any possible combination, that's 256(?) combinations, perhaps even that many endings. That's a lot of renders even if you only do 1. The other option is to render each girl in a pose and have them stacked ontop of each other for a single final render, where who you end up with determining whether they appear, but that's not always valid.
More girls you add, more work there is to do. Sometimes, the amount of work isn't worth the ultimate effort. Ultimately up to the Devs though.
The other complication is when, you try to drive plot through romance. Take Man of The House for instance, quests for one girls can be the gate to a quest with another. I can't get my sisters friend without fucking my sister first, that works for both sisters and both of their friends. If I like the friend but not the sister, I'm prevented from accessing that content without going through content I don't want.
Some devs will have options to get the same result without the gating, others require it. One has the advantage of choice, the other plays a more vital role in story / plot. When a Dev has a plot point tied behind a Romance or Sex scene, then they'll want to force it on you because you need that plot point. I myself, personally sit on the side of, "Why would Sex be the requirement for this plot? Maybe change your plot."
But alas, it's ultimately up to the devs.
My last words on the topic are quite simple. Force ANYTHING onto a player, run the risk of them hating it. Put more work into the Freedom of Choice, and players will be able to avoid what they dont like to focus on what they do, thus decreasing the chance of them hating it. Take care in forcing anything, decide what has to happen and what is more flexible and then make your final decision.