This was something I considered very recently (when I realized my only remaining VGA monitor didn't support the oddball frequency put out by an old Supermicro server on which I was still running something important).

Some pros of laptop servers:

* Quiet.

* Low-ish power consumption.

* Doesn't take up much space.

* Built-in secure console.

* Built-in UPS.

Some cons:

* Limited in what drives you can put in it. Some laptops only support one drive, so you can't even do RAID mirroring. A real server will usually let you put at least a few high-capacity 3.5" drives in it, on SATA or better.

* Many laptops will overheat if run with the lid closed.

* If you get a burglary, a laptop is very likely to be stolen. (In a rack in a city apartment, I bolted down the servers with security head screws, and there was no way they were taking the whole cabinet, with a huge APC UPS anchoring it down.)

Slightly newer one here (Lenovo T470). The battery still works so it’s got a built in UPS. KVM comes with it too!

All it does is scrape jobs really. I was running it on a VPS but that requires a modicum more effort to keep secure. This thing is a rotting unpatched Debian 11 and is behind a NAT with no service ports exposed on public interface.

Been using old laptops since HS. Remove the suspend on lid close and throw that thing in a closet.

You can always find free/cheap laptops.