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.
Yeah, my power bill is pretty reasonable already, considering my large family plus all the electronics I run. I just like seeing what everything is doing as a matter of curiosity.
Oh yeah, as a hobby, it's absolutely fun. I like tinkering with all kinds of things.
My point was to just be careful since it's not necessarily going to be worth the expense and time.
I've been considering getting a breaker-level power monitor to watch for spikes. It's a bit more expensive (hundreds of dollars), but it measures the types of things I'm interested in. My kid flipped on our gutter heaters (I never use them) and shot our electricity bill to the moon for a couple months until I noticed. If I had a home energy monitor, I would've noticed a crazy energy spike and that might have paid for itself.
Yeah, I never expect a financial ROI for hobbies; the ROI for that is nothing more than my own enjoyment.