Originally Posted by DLCS
If you mow wet grass for 5 minutes, you will have grass sticking to them. I'm not talking long clippings but the stuff that gets caked on from the center hole to where the cutting edge starts. Unless you scrape all that stuff off, you will not have a accurately balanced blade. I haven't balanced a blade for a few years, no problems to date, and no vibrations.
It should stand to reason that you need to clean the blades a little before you sharpen them in this case. However; the caked on stuff should also be somewhat evenly distributed on the blade since it is spinning at a very high speed.
I don't think I would want to trust the plastic cone balancers too much. They are made of pretty cheap plastic. They do make metal ones that seem to be a little smoother operating and likely more accurate.
Any time you spin that piece of metal the size of commercial mower blades, with that kind of weight, I can't see how anyone would think that it wouldn't hurt the bearings that support it. Maybe not over night, but they will wear out much sooner than they normally would. The vibration that they would cause would be somewhat isolated by the chains, or other linkage that support the deck. You wouldn't likely feel that much of it, even if was fairly bad. You may not notice it at all with all of the other vibrations that the machine is making.