At some point, the efficiency of new hardware completely outweighs the benefits of keeping old hardware running. Obviously there's a valid need to preserve hardware for historical purposes, but for any other reason I think it's a false economy.
The CPU on a Raspberry Pi 4 is nearly three times faster than a 3.2GHz Pentium 4. A Raspberry Pi draws no more than 10W (excluding USB devices), but the Pentium 4 has a TDP of 100W. We could draw a parallel with incandescent vs LED lightbulbs, but I think that would be too kind to the old computer - an old motherboard and a discrete GPU will add substantially to the idle power consumption.
The CPU on a Raspberry Pi 4 is nearly three times faster than a 3.2GHz Pentium 4. A Raspberry Pi draws no more than 10W (excluding USB devices), but the Pentium 4 has a TDP of 100W. We could draw a parallel with incandescent vs LED lightbulbs, but I think that would be too kind to the old computer - an old motherboard and a discrete GPU will add substantially to the idle power consumption.