As long as you are re-balancing the blades...I still sharpen blade with a grinder and then balance them. Of course I go though a stone every few years. And some blades are simply cheaper and a lot less time consuming just to replace them.For a home-owner, no sharpener is going to pay for itself, especially a $200 sharpener. But I just like to do things correctly. But I cheat in this case. Free-hand is good enough.......
Yes...Some of the blades I seen are really bad. I even had one 21" Honda mower that came where to blade only 12" in length as it was that worn. A total loss but that not why the mower came in for. It was the knocking that the top crankshaft bushing was causing due to it being completely worn out.
Don't have a lot of control over what customers bring me. Plus time is money in a shop.
For a homeowner who doesn't want to spend much money the hand file will work if whey don't let them get too bad. In my shop working for a customers I use an angle grinder. I just don't know how an 21 in. blade can wear to 12 inches, something I would like to see.