By spending the coins as they arrive, I'm not spending in my current account or credit card, which means I don't need to pull that extra cash through from savings. In effect, my real "coin jar" is my bank savings account; a better place for loose change than my desk!
I do like the illusion of "bonus money", but prefer the real (pitiful) interest earned - should cover a pint of milk every five or six years
VRD