I started loading my own 12g a couple of years ago. As a few others have said the savings are minimal, but what it does allow you to do is customise your loads. I use 36g 5’s and 6’s for game. I do 38g 4’s for ducks and 50g 3’s for geese. Normally in a commercial cartridge when you go up to 36g the shot size steps up to at least a 4, which is too big for pheasants. So if that sort of thing appeals to you then it’s worth doing.
cheers
Greg
Went down the reloading route for the same reason, was very surprised once I started to test patterns that a slower load actually worked better in my gun.
Furthermore, if you have a semi-auto (long recoil) you can tweak the load to run more reliably with less felt recoil.