Compared to what? At least it used to be that running in PC mode disabled almost all if not all image processing which is usually what causes input lag. At least I have never noticed much difference between game mode and PC mode when I have tried this before.In my experience game mode on and off is a huge difference, and then on top of that, turning off the "Boost" mode also makes a big difference. I tested this out in multiple games just panning around. It's really noticeable, unfortunately.
Boost mode AFAIK only works in 60 hz which is probably more relevant to console gamers than PC gamers.