You should sharpen your bush hog blades whenever you notice the bush hog is not cutting properly, or becoming heavily clogged with torn debris. A dull blade will pull tough stalks instead of cutting them, and they could wrap around the output shaft of the gearbox and ruin the seal in the gearbox.

How sharp should a rotary mower blade be?

Mower blades should be aggressively sharp, but not as sharp as a razor's edge. You should be able to touch the blade with your hand without getting cut. Contrary to popular belief, a lawn mower blade with a razor sharp edge will not cut grass better.

Can you sharpen a brush cutter blade?

Blades can be sharpened by hand or with the machine. The machine sharpening is obviously highly effective but doing it manually with hand also could be appropriate (will take a good amount of handwork).