tablet provides absolute tracking and mouse provides relative tracking, so you can "line up" where the notes are on the screen proportionate to your tablet area. it takes a while for a lot to adjust to but I feel so much more control with a tablet pen opposed to a mouse cause I hate relative tracking.
there are some great mouse players though, SiLViA and cptnXn are both phenomenal and are famous for using mice to play
also pretty much every osu player uses the keyboard, both tablet and mouse players. tapping on tablet sucks ass and clicking on mouse is pretty bad too. you can use Z/X or whatever keys you want to bind them to click notes, much more efficient but can take some time to have your two hands in sync
also i love this song you should download it