Decoration.
I tried putting my lighter in there once, but because I don't have tiny fingers the size of tweezers, I couldn't get it out again. I had to take my jeans off and squeeze the lighter back out of there. Not very practical for public use lol
I tend to keep important stuff - small bills, taxi recipts, notes and cards... and then forget about them. They become lint, later, when they go to the laundromat. :P
Put my car key in there when I'm in public places and don't want my car keys pick-pocketed. I'm a little paranoid about that after I ran into some gypsies in Spain a while back. Being "gypped" is not racist. At least not if you're me.