A ridiculous example would be a few posts back, someone wanted to be able to hot key every skill, alternate weapon, scroll and potion in the inventory. I can't remember what I had for breakfast last Monday, and I likely also won't remember if my summon Spider scroll is hot keyed to bar 9 slot 7 or bar 7 slot 9.
This my wow skill bar from IDK how many years ago(WoLK) :
Not only are there far more abilities available, they take up very little of my screen and I have keybound most of them(over 40) and could use most of those fairly quickly in combat. People can learn/develop muscle memory for quite a few keys and it can dramatically improve fluidity and convenience of combat to be able to do so.
All I really would ask for in D:OS though, since it's turn based and we have all the time in the world, is just to conveniently have all my combat skills on the screen at the same time to be able to click them in a timely manner and not need any excessive extra steps to access them.