Most TVs and monitors have a fixed refresh rate, often 60 Hz these days.
If a game runs at, say, 48 FPS, some frames would be doubled every second, and some won't. The resulting video would seem more jittery compared to 15, 30 and 60 FPS, where frames can be doubled or quadrupled evenly.
That's why FreeSync and G-Sync monitors are a big deal to enthusiasts, they avoid this issue for their refresh rates are exactly what's being rendered.
Edit - in certain hardware configs, some games could still feel more fluid at, say, unlocked at 40 FPS than locked at 30 FPS. But that relates more to uneven frame times, and not the framerate itself.Last edited by haxxiy - on 26 May 2019