I have always sharpened them so you could shave with them. If you sharpen them to within 1/8, they are not sharp, so why even bother. I even sharpen and balance new blades. Just because they are new, doesn't mean they are balanced either. The best balancer I've used is posted on a thread called USA and Canada team up. Just do a search on balance and go to that discussion. Just don't get blades hot while shapening them and they stay sharp for 4 hours normally. A professional blade grinder turns at a slower RPM to help prevent overheating of a blade, but you still can get them to hot if you don't move the blade while grinding or move it to slowly. Cutting grass with a dull blade is like cutting up a turkey at the Thanksgiving Dinner with a butter knife. You can get the job done, but it will just shread it. It is easy to spot a lawn that is cut with dull blades. There is one lawn company in our area we call
The Lawn Killers, because their lawns always look brown, even when we are getting lots of rain. If you examine the blades of grass, they are shreaded and some don't even get cut off. It just knocks the grass over and you see an almost cut off spot in the blade of grass. Several times a new customer will tell us, our lawn looks so much greener and nicer since you started cutting our lawn.

Sharp Blades are best, in my opinion.