Homeplugs (ethernet over power) are fine for some things, but they add so much latency to the network.
Wired is so much better.
Powerline communication uses adapters to transmit network signals over existing electrical wiring, avoiding the need for new CAT6 cables and offering a hardwired internet connection in hard-to-reach areas where running Ethernet is difficult or impossible (or where the house owner simply is too lazy).