It’s a personal preference but I would take occasional smearing over janky frame rate, I don’t know why but if you are not a solid 60,90,120 it just feels really like there is a stutter every second or two even though it should be fine if it’s above 60fps.

For some games I’m happy to turn it on as it drops power/temps and provides virtually identical output (as far as i can tell anyway) to native, but my fans don’t need to go into overdrive mode.

I may even put on frame gen too if I just want to bump a stable-ish 80-90fps to stable 120fps, and again drops power and temps slightly. That sometimes does cause smearing but for the most part I don’t notice enough to be annoyed. Without them I would probably be running with more power draw and higher temps, and possibly still not even hitting lower resolutions at 120, some games as you say though can hit 120 no problem even without and the gpu won’t be stressed.