For the keys. Where could the key ring go for, right? But it's not that clear. Do you know when you throw your backpack in a bunch of others? It's perfect if you recognize it before you unpack your winter jackets for a summer vacation by the sea and someone else wears your swimsuit on a trek in the Pyrenees. So, the key ring is also a backpack ring. And sometimes a bag ring or a suitcase ring, huh?
Just a differentiation that you can pin on anything in no time. Most often, it ends up on keys. On a motorcycle, on a scooter, from a house or a rehearsal room. You can recognize them reliably and easily fish them out in your pocket.