This is an awesome question. This important task is often overlooked and can lead to stressed turf and an entry point for disease activity. When a lawn is mowed with a dull mower blade, it may shred the end of the grass blade causing the lawn to appear off-color. Image just one grass blade that is white on the tips from being shredded, now multiply that by thousands of blades and you can quickly see how that can affect the color of your lawn. In addition, this shredding of the blade takes time to heal and during this period fungal activity can find its way into the plant much faster. It is good practice to sharpen your mower blade every five hours of use or once a month. You can take the blade in and have a pro do it or you can invest in a few tools and do it yourself. The key is to make sure the blade is balanced after you sharpen it. A balancing kit can be purchased online. A clean-cut is a healthy cut. (Be sure to disconnect your spark plug when removing the blade. Safety first)