I suppose it depends on the couple. I've been in different situations where a video got us in the mood, though once where it killed the mood (more on that below).
I've known guys who see it as a distraction while in bed, others who want to copy all the moves. And my late partner, possibly out of insecurity, got mad if I even looked at nude pics online, considering it a kind of insult to him and almost cheating. But I loved him too much, and he gave me all the sex I needed, so I didn't miss the porn.
The story: I tricked with this guy briefly when I was a recently-out newbie, and the first time over at his house was a little awkward. I've never been as sexually aggressive as many guys anyway, and neither was he, evidently, so getting started was slow going at first.
Finally he sat us down on the sofa and put a gay porn tape into the VCR. It turned out to be the most gawd-awful attempt at a military barracks scene, that he thought would appeal to me because of my former career. But I found all the mistakes & flaws too distracting, like the impossibly long non-regulation haircuts, the laughable uniform errors, the Army "bunks" that looked like something from Ikea, the silly dialogue no soldier would speak.
Finally he got mad at me for playing film critic instead of getting into it. I realized my mistake, because he'd thoughtfully done this just for me, and I apologized, and said a non-military tape would be better for me. He started one, and soon we had our dicks out stroking ourselves, then stroking each other, and finally naked on his bed, the video left behind.
Porn can be a sexual stimulant under the right circumstances, but a killer under the wrong. Gay porn in an LTR is like anything else: a matter of mutual agreement & accommodation. Anything that pleases both partners is fine; anything that doesn't needs to be negotiated or else nixed. If either partner won't budge, then maybe it's not a good match.