Why is communication not established without TURN in webRTC?

Question

WebRTC

Tell me who knows, without TRUN webRTC should establish connections in different networks?
I looked at the code of a couple of well-known roulettes, they have only one, two STUN servers are transferred to RTCPeerConnection ().
For me, without TURN, it only works on the local network.

Answer 1

Because it is not always possible to break through NAT, just in case, a TURN server is taken, and it already works as a relay.