The author is not wrong, there is a lot of old hardware out there that is still more than serviceable for many things. But the loaded cost (power, maintenance, space, etc) of running servers at "home" can be way more than the $10 a month for a droplet on Digital Ocean.
What I'm saying is that the math isn't as straight forward as it might appear.
That said, it is now pretty straight forward to build a 'nano-datacenter' consisting of an enclosure, thermo-electric cooling, rack, switch, UPS, a server providing NAS storage and a couple or 6 servers providing compute. Plug its PDU into the socket where your dryer used to plug in out in the garage.
What I'm saying is that the math isn't as straight forward as it might appear.
That said, it is now pretty straight forward to build a 'nano-datacenter' consisting of an enclosure, thermo-electric cooling, rack, switch, UPS, a server providing NAS storage and a couple or 6 servers providing compute. Plug its PDU into the socket where your dryer used to plug in out in the garage.