This is similar to other requests (different watchface for quiet time, different watchface based on time of day, etc), but also slightly different.
I have a few watchfaces I like to use when I’m actively looking at the watch (they’re very pleasant visually) but whose animations etc are wasted when the watch is in standby mode. It would be nice to either allow the display to turn off entirely in standby mode (maybe with a screensaver or something) or select a different watchface for standby mode.