By capping I can reduce the GPU usage, so my CPU can spare more horsepower calculating Background NPC's in big towns. At least, I think that's what I'm doing. I only know what I've tested and capping my framerate gives me a complete stutter reduction in towns. When I uncap my framerate, and therefore clear my GPU to go full-force, I notice clear stutters in scenes with many NPC's. Just a matter of finding the perfect balance between GPU usage, framerate and performance.
But I also notice the fluctuations pretty well when my framerate varies in the 30-50 fps area, so I'd rather still cap my framerate a little above my average fps value (which is 45-ish). This doesn't make the framerate fluctuate that much. I do agree that you don't really need to cap anything, but I'm almost never getting more than 50 fps anyway, so capping at 45 just gives me an overall smoother performance without losing anything. Yeah, 5 frames, so what. A capped 45 fps with G-sync is, for me, a much smoother experience than a G-synced framerate which still varies wildy. Sure, there's no screen tearing or input lag, but you still can tell when your framerate goes up or down. At least that's my experience, but I'm weird.
