RTCPeerConnections generate and parse SDP according to the standardized format. Exchanging SDP is needed to set up calls in WebRTC. Following the standard is important for cross-browser interoperability. Unified Plan also enables the RTCRtpTransceiver APIs. Changing from the old ("Plan B") to the new format can cause backwards-compatibility issues or break applications, see the Transition Guide: https://docs.google.com/document/d/1-ZfikoUtoJa9k-GZG1daN0BU3IjIanQ_JSscHxQesvU/edit?usp=sharing
Docs: https://docs.google.com/document/d/1-ZfikoUtoJa9k-GZG1daN0BU3IjIanQ_JSscHxQesvU/edit?usp=sharing https://webrtc.org/web-apis/chrome/unified-plan/ https://tools.ietf.org/html/draft-ietf-rtcweb-jsep-24