It's unlikely you'd want to connect IOT devices to a backend using web sockets, I'd use a UDP based protocol for that, e.g. QUIC. But for web clients it makes sense.

MQTT is usually the go to protocol for IOT devices. You can do MQTT over WebSockets to help prevent issues using odd ports on home networks etc.

This was working for Peer5 (YC startup) - building a p2p CDN, these were video viewers in live events (e.g. the world cup).