With clipless pedals your shoes have these cleats on the bottoms so you can clip in. usually they are a little recesses, but after walking around they begin to meet the pavement. My current “work” shoes have worn down so much that they no longer stay clipped in on my pedals. I really like to hear the crunch crunch.
The real bummer is that the screw heads are worn down as well. I have to get a new pair of somewhat decent looking shoes that I can wear to work.