Look there's been a lot of arguments made for both sides of the issue. I personally think that sharpening lawn mower blades is more cost affective than buying new ones. Of course you run the risk of removing more material from one side of the blade than the other and throwing it off balance. There's also the concern of damaged blades being perpetually reused after hitting things while mowing that they aren't intended to hit (stumps, bricks, steel, etc). Warped blades can also lead to off balance performance, wear on the mower shaft and in turn the mower, and a less than manicured look for your lawn. Hairline, microscopic cracks could also be lurking, just waiting for the right moment to fly out like a Steven Segal thrown katana and take somebody's head off. Alas, in the end, i'm a cheap skate. So I think the risk of a poorly groomed yard, prematurely worn out mower, or even the off chance of decapitating an unexpecting neighbor are worth the risk to save money on blade replacement. I mean nobody really talks to thier neighbors any more any way.