The root system of your lawn needs oxygen to function. A heavy clay soil, or one that is compacted from foot traffic or rain accumulation, severely impedes air exchange and movement. When this happens, oxygen cannot get to the root system, and your lawn begins to show symptoms of slow gradual decline. The most obvious result of compaction is a lack of growth and thickness. With many homeowners there is a belief that grass clippings result in thatch build-up, and that there is a need to bag clippings to keep the lawn clean and more healthy.
Clippings are ninety percent water and break down quickly.
Try to cut your lawn more frequently so that clippings are shorter and will not accumulate in clumps on the lawn surface. Thatch is the other problem resolved by core aeration. Thatch is predominently the build-up of dead and decaying root systems. Thatch can be so dense and impenetrable that it can deny water to the root system. Once thatch gets to over a half inch in thickness it is a serious problem.