If you reload the cheap Winchester and federal hulls (the ones all over the ground for free anyplace people shoot shot guns) and you use clay buster wads, you can load very consistent ammo on for a little less than what you can buy it new. But, can you always get the same cheap stuff new? Sometimes it's 1 1/8oz, sometimes it's 1oz, sometimes it's unavailable all together. I like to load up 3/4 and 7/8 oz 12ga trap shells. They are much softer shooting, but are rarely available for purchase.
For me it makes sense. Maybe not from a cost perspective, but from a consistency and versatility perspective. Plus it's fun!