I just watch the scenes like independent scenes. I don't care that KATU-084 (for example) has 3 different scenes. To me is the same KATU-084-B than LULU-104-C.
To be honest I don't get the question. I've never watched a porn video like it's a film. Sometimes I'm interested in a full scene (I mean, the typical movie scene, not the 40 mins scene) and I watch it, but the normal thing is that if I want to jerk off I end up opening 4 or 5 videos.
If you want to watch the 3 hour of a movie... it's ok if you want it that way. I, on the other hand, assume that I'll return to that video a lot of times so there's no point watching the full scene.