It doesn’t have to be. I have a proxmox homelab, running x86 openwrt in a VM. It has many other services running including home assistant. It idles at 3% CPU and consumes around 5w. I’m using a Levono thinkcentre.
Otoh it would make sense if you could combine it with a home server, then it's just a side process and you actually save power by not having an extra device.
Though you'd still need a switch or two. And a fiber modem which already has a router and a switch built-it. Oops.
