Babs, I also do what Grame said, I always fill the canner and sometimes it is with a jar of water, i use saved "used" lids, if they don't seal, no loss. figure I have to store the jars anyway, might as well have them full of water in case I need it. Also, when i re-use the lids they seal just fine. So far this year I have had one not seal out of 20+.
I am not loosing anything if the lid doesn't seal, and I am gaining some water storage if it does. I have been doing this about 5 years now. when it is time to can food in the jars, I just open and dump the water onto the garden. really helps in the jar washing department too. no surprise spiders have taken up residence, or dust in the jars. so much easier to wash them and can. to me this is a no-brainer.
for me it is just an easy way to make use of expensive lids, and space.