I'm not familiar with WebRTC. What's the use case there? I can't remember ever wanting to create an in-browser p2p connection on my local network. What would it be used for?

Please read the Chrome 48 release notes, WebRTC's default behavior has changed. https://groups.google.com/d/msg/discuss-webrtc/_5hL0HeBeEA/H...

But it still ignores the proxy settings and will use STUN to discover your "external IP". Thus users that think they are using a proxy end up not actually doing so.

WebRTC is a secure real-time protocol for audio, video, and data.

You'd want to use it any time you want a high-speed network connection with another user. For example, a multiplayer game or video teleconference.

in-company hangouts, video conferencing, etc. Without p2p on local network that would have go outside the company and back in.

Others have pointed out this behavior has changed in Chrome 48. You don't get the local IP unless the page asks for access to the mic/camera which the user has to give permission for.