A dull blade can be sharpened, but a blade that is worn out, bent, cracked, or otherwise damaged must be replaced. Because damaged blade can become dangerous projectiles.
Thrown objects can cause serious injury. Inspect the blade(s) regularly.
Do not operate the mower with a worn or damaged blade.
Picture below showcases different stages of lawn mower blade. If the condition of blade is below NORMAL, it is recommended to replace the blade.
RELATED – Looking to sharpen lawn mower blade? You can DIY, learn more here.