I think it is a level 1 version of fork (level 2) and splitter (level 3), and it is (almost) useless.
It that were true it would be useless indeed.
(Maybe you could use one if you have only one fork and want to use something which needs three sockets on the same circuit.)
That doesn't work because the relay thing gives you only one socket. If you have equipment that needs 2 or 3 sockets just link them with socket links. I asked the author about it but haven't received a reply yet.
Well anyway I finished the game just a few hours ago without using a relay socket. So obviously it's not necessary but nevertheless I'd like to know what it's good for.
The game has much potential but needs more detail, more features and better balancing. The start can be very hard while later on the game gets too easy with more sockets and equipment. I think it would be cool if the game took some inspiration from good old Paradroid (C64, Amiga) like hacking into enemy robots and taking them over.