I thought this video was rather interesting, because at 12:27, the presenter crunches the numbers to find out how many years it would take for a new computer purchase to be more environmentally friendly (in regards to total CO2 expended) compared to using a less efficient used model.
Depending on the specific use case, it could take as little as 3 years to breakeven in terms of CO2 if both systems were at max power draw forever, and as long as 30 if the systems are mostly at idle.
I love this community, I used to rant about efficiency all the the time on reddits self hosting community and everyone thought I was insane. If the damn thing is going to run 24/7 for 5+ years then put a little thought into its power usage!
I personally love old Dell optiplex micros on eBay. Cheap, plentiful laptop hardware in a cute little box which allows modest upgrades. My primary server in a full sized case is just a laptop CPU, Ryzen 5600g. It brings me joy that my network has four servers and still is under 75w idle for everything including networking gear.
Yep, I moved my server off of my main PC and onto an N305 board. Now my entire server draws less power under load than my PC at idle.