well yeh… look at the title
i have no friggin idea what’s it for, ppl say it makes difference, well I don’t hear any 
Just try it for your self.
try put a closed hihat on every line in a track. Set the groove settings ex. 1=70% 2=0% 3=70% 4=0% and compare with 1=0%-2=0%-3=0%-4=0%.
If you can’t hear a difference I think your deaf. sorry. OH. You can also see the difference!
In simplistic terms, what the sliders set at different percentages is doing is speeding up and down the song, thus creating a swing type effect. It doesn’t have to be set symmetrical either, which could yield some interesting results. You can also save your settings much like saving a radio station on a car stereo.
The key to this feature is offsetting the sliders as cubedecibel illustrated. Make sure you also check the box in the far upper left corner of the frame.