well believe it or not if youre into really e-sports like world of warcraft having a mouse like that is almost a requirement for PVP.
for example if you play a death knight in WoW you have roughly 25 spells you'd use in PvP, which means you need to map about 25 buttons at a minimum to be able to map them all. Then you need to keybind certain macros, for example you'll have one button that casts Chains of Ice, and then another button that casts Chains of Ice on the person targeting your healer. It ends up being about 40-50 keybinds for some classes and having 20 of those on your mouse is actually pretty convenient in hectic fights.
