Power efficiency is very important to servers too, for cost instead of for battery life. But, energy is energy. Thus, I suspect that the power draw is in userland systems that are specific to desktop, like desktop environments. Thus, using a simpler desktop environment may be worthwhile.
It's important but not relative to performance. Perf/watt thinking has a much longer history in mobile and laptop spaces. Even in servers most workloads haven't migrated to ARM.
I used Ubuntu around 2015 - 2018 and got hit with a nasty defect around gnome online accounts integrations (please correct me if the words are wrong here). For some reason, it got stuck in a loop or a bad state on my machine. I have since then decided that I will never add any of my online accounts, Facebook, Google, or anything to Gnome.