When I was a student in high school (all too many years ago, alas) The church I attended (built in 1926) was full of these edison sockets, complete with brass plates, most of which had been slopped over with several layers of paint. There was also a very noticeable absence of ordinary 2 wire duplex (or single) receptacles. I think this used to be the common way of connecting portable equipment (lamps, fans, irons, etc.), by using a device which had a screw shell with two wires extending from it, spliced to the power cord of the equipment. I guess if one of these wall sockets was not within easy reach, you could unscrew a light bulb from a nearby ceiling fixture and connect there instead.
Electrical safety has made some significant advances since that time...
The Orange Co courthouse has these all over the place, I thought they were just some funky decora device I'd never seen before that had a ridge between the 2 outlet openings.. (Well, I guess they ARE a funky decora device when it comes down to it LOL)
I've got some old Bryant toggle switches that I pulled from a house dating back to the era of the edison base outlet (1927) but all the outlets in this house were regular NEMA 1-15 or 2-15 (the T slots) made by Arrow Hart.
When did use of the edison base outlets seem to end? I've worked on houses and buildings dating around turn of the century and have yet to come across one here.