I use it as an attachment point to hold my paracute cord and a carabiner or two. I haven't found much other use for it.

You can kind of see it here on my small pack:




I've seen some guys use it to attach their camera bag or other small bag with stuff they might need to find/access quickly (first aid kit). I've also seen extra-large blades attached there, since they are too long to stick in the pack and too awkward to carry on a belt for a hike.


I believe they are modeled after the military MOLLE/ALICE attachment system that lets troops attach radios or other accessories to the outside of their packs with special clips.