Every time I go outside, there's like 2 out of 10 people who have headsets with them, listening to their playlists using their phones. That's a very common sight already, specially with everyday commuters who are sometimes stuck in traffic. These audio connectors can be a need for them sometimes. :)
3.5 mm audio jack is the most common one that we see everyday because this is the one that usually fits our phone's audio device. However, this audio jack isn't just limited to our phones' devices. In fact, we can also convert 3 5mm to dual rca, I've seen Dane do this so many times on his guitar amplifier when he wants to use it as speaker for songs.
I don't know much about the technical side of connectors but all I know is that they've become more and more important each day. :)