Mowing heights is based on the growth habit of the grass. Some grasses grow long and strait, others low and wide. Cutting the lawn at the right height is important. Edging is growing along all the driveway and sidewalk lines were the grass meets with the concrete with an edger. This gives a nice clean crisp look to your lawn. Trimming is the task of going along fences, houses, planters and other objects in the lawn.