I think the introduction (invention, discovery?) of this protocol (and its associates) is what made all audio and video calling IP programs we have today (there are dozens - Skype, Zoom, Facetime, Messenger, and dozens more) possible.
I remember the problem at the time severely limited deployment and use of programs like NetMeeting.
https://en.wikipedia.org/wiki/STUN
By Christoph Sommer - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=1337756

