Not a dev, but I have 3 monitors on my rig that I use for work and play.
A 24" 1080p as my main monitor for stuff like games or Blender, a smaller 18 and a half inch 720p for secondary stuff like Firefox, Discord/TeamSpeak, and monitoring Cura when the 3d printer is going, and a 21" 1080p Wacom on a monitor arm. The Wacom is kinda outside my field of view unless I'm actively using it, so most of the time it just has a performance monitor running so I can see what's hogging my resources. Having Spotify on there is nice though, the touchscreen/stylus makes running it quick and easy.