A lawn edger is specifically designed to cut through the edges of grass and along the edges that flank your lawn, such as driveways, walkways, and flower beds. As such, you can expect a lot better results with a lawn edger. With sheers, the edges likely won’t be even and you could potentially cut too deep into the roots and damage your lawn. Not to mention the fact that you’ll need to exert a lot more energy when you edge your lawn with sheers.