Buried away in the Display section of the Accessibility controls in macOS Sierra is a new option: Reduce Motion. It’s intended to help those who get slightly seasick with all the zoom animations that have increasingly come to define the Apple user-interface experience over the last decade.
To activate it, open System Preferences, click the Accessibility icon, and then select the Display icon at the left. Then put a check in Reduce Motion.
Alas, it doesn’t do a great deal. Windows still minimize to the Dock in an animated way, for example. Calendar pop-ups also continue to, well, pop-up. All it seems to do is turn off whole-screen zoom effects, such as when you enter Mission Control, and when you activate LaunchPad. The zoom effect is replaced with a subtle crossfade. It also turns off the zoom effect when you select to reveal the desktop (i.e. Cmd + Mission Control key), and turns off the zoom when you make an app fullscreen.
Rather strangely, the existing Reduce Motion control that appears in the Photos app’s preferences dialog is still there, and seems to operate independently – turning on the option in System Preferences will not turn it on in Photos too. (Perhaps more evidence of empire building amongst the teams at Apple? But that’s another topic for another day.)
If you spot any other visual effects that are curtailed by turning on the Reduce Motion feature, please mention them in the comments below.