One of my servers is only there to connect my HP LaserJet 6P.
I've had that HP LaserJet 6P for more than 25 years, and it's given good service all that time. But the only port it has is an old-fashioned parallel port, and computers today don't have parallel ports. So I used an old computer to run the HP.
I tried using a parallel to USB cable, but that didn't work. And then I had an idea. I went on eBay and bought a second hand JetDirect 170X for £19. It arrived today. I plugged it in and powered it up, and pressed the test button, and it told me that its IP address was 172.22.28.190; presumably that's the IP address that the last user set it to. So I unplugged it, held down the test button and powered it up again, holding the test button down for several seconds. That did a factory reset.
When I rebooted it, it used DHCP to acquire an IP address of 10.14.63.23, because my whole network uses addresses in the 10.x.x.x range. That's better, and I was able to access it. I tried to use the web interface, but it wanted a prehistoric version of Internet Explorer or Netscape, so instead, I used Telnet.
I disabled DHCP and set the IP address to a fixed value so that various computers would be able to find it. And it all worked!