I'm in the process of getting my Home Assistant environment up and running, and decided to run a test: it turns out that my gaming PC (custom 5800X3D/7900XTX build) uses more power just sitting idle, than both of my storage freezers combined.
Background: In addition to some other things, I bought two "Eightree" brand Zigbee-compatible plugs to see how they fare. One is monitoring the power usage of both freezers on a power strip (don't worry, it's a heavy duty strip meant for this), and the other is measuring the usage of my entire desktop setup (including monitors and the HA server itself, a Lenovo M710q).
After monitoring these for a couple days, I decided that I will shut off my PC unless I'm actively using it. It's not a server, but it does have WOL capability, so if I absolutely need to get into it remotely, it won't be an issue.
Pretty fascinating stuff, and now my wife is completely on board as well; she wants to put a plug on her iMac to see what it draws, as she uses it to hold her cross-stitch files and other things.
7 months later update:
I've expanded HA quite a bit and have a decent grasp on where my electricity is being used. Suspending my desktop has saved a shitload of power: under Linux, when suspended, it draws ~10W of power at any given time vs ~100W when idle. Also, I put smart plugs on the server cluster; the total usage of the entire cluster - 4 mini PCs, 1 SFF, and 5x HDDs (NAS) - over the last 7 months so far is currently at a whopping 465 kWh. That's ~66 kWh a month. Barely 5% of my monthly electrical usage.
My desktop PC idles quite high as well. The semi high-end consumer motherboards on the AMD side tend to use a lot of power at idle, so I think that's a big part of it (at least the x570 series, can't speak for later). And as others have said, high refresh rate and multiple monitors can make things worse.
I'll add though that people's perception of how much power there system is using can be skewed by software based monitoring tools. People may think there system is using only 50W because that's what software reports but it's actually drawing a 100W at the wall.
My X670E system also uses a shitload of power. Literally 150w at idle, no matter what I do. Tried disabling every unnecessary feature in the BIOS and enabling all the energy efficient settings I can find, to no avail. Drives me nuts.
I'm eyeballing HWINFO64 right now, it's saying my GPU is idling at ~28W and the CPU is idling at ~36W. Add a couple watts for the fans, various peripherals, and waste heat; it's close to what I saw earlier.
The dual 1080p monitors eat up about 30W apiece on their own, when powered and actively displaying something. Barely a watt or two each when in standby mode.
36 Watts idle sounds like a lot for a 5800X3D. I'll see what my 5700X3D does, never checked that. Not in software and not at the wall.