I needed to join two pieces of copper pipe.  So, I went to the hardware store for a copper fitting.  I started to pick up the one for $1.29 but then I noticed the one for $0.59.  The difference between the two is that the cheaper one has a dimple in the center and the expensive on does not.  Since either one would work for me,  I chose the cheaper one. I am at a loss as to why anyone would want the expensive fitting.