You install VirtualBox or Ganeti on it, create 100 VMs for various purposes for your company. Build Agents, Spikes/PoCs, any and all purposes. Its like a cheap local cloud.
I honestly have no idea why "home" servers are so bloody loud. My desktop is more powerful than any of the machines at my company and it doesn't sound like a jet turbine--even at full load. And even when our servers aren't fully spun up, the fans are so loud and droning even at lower RPMs!
Is it an issue of "overpowered" fans (for really hot rooms), or is it really just an issue of "cheap as crap" fans by OEMs?
It's the physics of the volume of air that is being moved by the fan. A 2U tall fan has to spin twice as fast to move the same volume of air as a 4U tall fan. A 4U is roughly the same dimensions as a full height desktop or workstation. They probably employ lots of 2U servers.