About half a year ago I bought a used UPS. It didn’t have enough output to power my main PC, but it’s perfect for my home server and network.
Starting on Christmas eve and continuing even today, my neighbourhood has been getting intermittent brownouts. It’s only affecting one phase (house is on a three-phase 240V connection), which happens to be the one powering my network (also all of the light fixtures, stupid Soviet house), and the UPS works beautifully. I didn’t lose any of my services even once. Without it, I would probably be reinstalling Proxmox and praying to the RAID gods to restore my hard drives.
“It pays for itself as soon as it is needed” is proven true once again.
In Belgium it’s still widely deployed. Two other downsides are the risk of electrocution with monopolar switches (can’t rely on a light switch, not that you ever should but lots of people think “no light = no zappy zappies” then get a nasty surprise), and compatibility issues with some 3-phase appliances that aren’t designed to be hooked up without a neutral because they were not sold in an area where 3x230 is common.