I turned it off. The primary reason is that I use ctrl+arrow keys to move between workspaces frequently.

These might seem unrelated, but:

* There's a `defaults set` setting that allows you to speed up the transition animation length from 1 second to 0.5 second, which is huge because that transition is extremely poorly implemented (it leaves the windows on the workspace that you're leaving activated until the transition is complete, so you start typing and it's on the other screen you can't even see any more) and VERY SLOW

* That setting only works if the refresh rate is 60Hz, and it completely fails to do anything if ProMotion is on, because for some reason the animation length isn't programmed to handle the different refresh rates.

So having ProMotion off relieves frustration.