You don’t really need more for most games, but two genres in particular really benefit - MMOs and military sims. Personally, in World of Warcraft, I generally had a lot of cooldowns that I didn’t use frequently but always wanted to have close by, and clicking those meant I wasn’t using the mouse for the camera. And in PUBG/EFT/etc, you’ve got all kinds of commands for zeroing scopes, chasing walking speed, using different inventory slots.
Also personally, I find ZXC awkward to hit regardless of where my hand rests, so it’d be nice to have more space on the left to rebind those if I wanted. I’m not bothered enough by it to do anything about it - just enough to chime in when I see a forum post about it.