Mulching lawn mowers make use of the nutrients from your grass clippings by finely cutting and re-cutting them within the cutting deck. These tiny clipping sar ethen allowed to fall into the lawn where they are concealed by the lawn but will wilt and decompose thereby feeding the root systems and helping to retain moisture. Mulching also saves time as you don't have to contuinually empty your grass bag, so no more bags of clippings, rotting piles of grass or soggy compost heaps (grass clipping sare notorious destroyers of compost heaps). The result should be a healthier lawn that you can cut in 70% of the time it would take if you were using a conventional mower.