We believe that the potential harm you can cause to your lawn by repeatedly cutting over leaves outweighs the potential benefits of leaving the organic matter on the turf. Sure, you are leaving an all natural substance on the lawn, which, at some point could benefit the lawn, but too much of anything is not good. As the chopped up leaf particles build up, they can actually smother the grass. This causes the turf to thin out, opening the door for weeds. The leaf matter does not break down fast enough to provide an immediate benefit to the lawn. For these reasons, we believe the leaves should be cleaned before any fall cuttings.