I just use one as a Plex server. Can't beat the cost of running it, which is roughly $6/year worth of electricity if I remember correctly. Previously I was running my Plex server on my gaming rig which cost a relative fortune to have running 24/7.
Do you otherwise not leave your gaming rig on? Me and all of my roommates leave our desktops on... they draw about 50-60W so abbout 1.5kWh a day which is less than 15c a day each. Perhaps your conflating the extra cost of the GPU activity incured what actively transcoding files? Which the Pi really can't do so Plex ends up just being a dumb DLNA server.
