I use it mostly for remote access to my Windows environment that I can't run as a VM. I would like to get a cell radio addon for true out of band remote access with one of the IOT type cell plans but I need to do more research on that.
It's good for critical systems that you might need to reboot and do things like see the BIOS (which you can't see if you're using a normal VNC-type remote access solution). It's probably not necessary for most setups, but it can be very useful in certain situations. I made one myself, then literally never used it, and I'm now using that Pi in a different project.
I thought about setting one up for my main server because every time the power went out I'd have to reconfigure the bios for boot order, virtualization, and a few other settings.
I've since added a UPS to the mix but ultimately the fix was replacing the cmos battery lol. Had I put one of these together it would be entirely unused these days.
It's a neat concept and if you need remote bios access it's great, but people usually overestimate how useful that really is.
Right, a KVM's usefulness is narrow and you're ideally using it as a sort of backup to a backup of critical systems. That means you usually only hear about them in server environments, and that means that sysadmins pay a LOT of money for enterprise-grade KVMs.
But it's very cool that we can build a dirt cheap, half-decent KVM out of a Pi nowadays. I might have just left mine running if I there wasn't a Pi shortage; I wanted that Pi for other stuff.