I don't game much anymore, but using a gaming mouse in my day-to-day workflow is huge. Besides the normal browser history-back/fwd, I have buttons for scrolling through tabs, closing/reopening tabs, alt-tabbing between windows, changing volume, etc. I don't make much use of macros or anything, but if I worked in CAD or Photoshop I'm sure I would. I think any kind of workflow that's hotkey or shortcut heavy could benefit.
I use a "gaming" mouse (Logitech G502) for day-to-day work. In additional to the usual left/right/middle click and up/down/left/right scroll, I have forward/back, copy/paste, next/previous tab, close/reopen tab, jump-to-first-tab, refresh, zoom reset, and microphone mute. It's useful enough that I find I really miss it when using a less-capable mouse.
How do you tolerate side movements when clicking side buttons and accidental side clicks when “rebasing” a mouse? How do you grip?
Every mouse I tried (suggested by reviews) does oops clicks sometimes, so I always turn off side buttons and live with the fact that they are just there discomforting my thumb.
I don't touch the side buttons when gripping or rebasing the mouse. That's not a G502 but every mouse I've tried so far (except for the G600) has been grippable without touching any buttons.
With the G502 your thumb rests below the side buttons on a small rest - to click you move your thumb up a little and then squeeze. The force required to click is still small enough that very light pressure from the other side of your hand is enough not to move the mouse.
I don't know other people, but I personally have never in the 10+ years I used "gaming" mice accidentally mispressed a button because I wanted to move the thing. Maybe logitech makes weird mice where this doesn't happen?
Hardware drag scrolling, combos and snippets, more configuration then you can swing a stick at, layers and all of that. Half of the reason I use QMK boards is due to on-host configuration being so so terrible. At least if I bring my own hardware I _know_ it's going to work how I expect when I plug it in. That's a huge sell if you are jumping between computers all the time and have hardware that fits in your purse.
Also, the form factor and things like the Ploopy Nano are super cool. And because it's open source if you don't like the hardware/software you can easily change it. We use interface devices all day, everyday. Not having an ergonomic interface will catch up with you.