The more direct problem in my experience is that all kinds of network devices that could reasonably be powered that way don't support it. My Fritz!Box router and repeater don't support it, my Sophos firewall doesn't support it (tho the Sophos XGS can supply PoE it doesn't seem to be able to be powered that way either) and of course the Hue hub and Raspberry Pi can't be powered by PoE either.