TURN Servers are designed to help certain users connect when they are behind a firewall or other network restriction. About 1 in 10 users need a TURN server to use OBS Ninja; if you are having problems, check to see if they are using the TURN server.
Sometimes, rarely, using your own TURN server can improve video quality for some users, if the public network routing is very bad and the TURN server is hosted on a high-quality private network, like Google Cloud. Details are provided in the code repo no how to deploy your own (turnserver.md)
TURN servers are NOT something you can use to share one video stream with multiple viewers. (That is an SFU server, which is out of scope of this article.) A TURN server acts like a middle-man, routing the encrypted data between two peers, mainly when those two peers are unable to speak directly themselves.