UPS is a mandatory for my desktop already, but all of them goes bad in a year or two, unfortunately. Which is why I am considering Laptops for server.
Laptops generally don't have the best thermals, so there's a limit to how much chooch you can get from them.
I am thinking of writing a script that will trigger the desktop to shut down as soon as the LAN goes down. My desktop is 1kw PSU, so, I am really not looking forward to replacing the 1.2kw UPS every few years.
These Laptops will be only doing backups, and small personal services
one for photo backups, replacing OneDrive
Another for sync, calendar service etc.
None requires heavy processing, in my knowledge. So thermals are not going to be an issue, hopefully.
Secondary issues are cats. And I don't have any idea how to stop them from stepping on the keyboards whenever they think like it, or jump on the router and cut the Internet :|
Does your desktop actually drain 1kw during normal operation? If so, yeah, it would probably benefit from a separate UPS. You might not need to replace the whole thing though, just the batteries -- admittedly they are the bulk of the cost.
WRT cats -- I got myself a network cabinet for precisely that reason. Also minimizes the amount of fur getting trapped in vents.