A healthy root system requires oxygen for respiration to support the plant above. The oxygen for roots is found in tiny pockets of air trapped between soil and sand particles. Over the course of the season, there are several factors that eliminate these air pockets. The most are eliminated as the result of compaction caused by traffic. The traffic from walking, playing and operating mowing equipment. 
     When the soil and thatch (the layer of organic material between the root and the leaf blade) become compacted or too dense, the pockets on which the roots rely are crushed, leaving very little air in the soil and making it difficult for water and fertilizer to penetrate. The roots are left gasping for air and nutrients. Eventually they wither and die; the whole plant soon follows.
     Aeration is the mechanical process that creates more air space in the soil and promotes deeper rooting, thus helping plants stay healthy.  This is achieved b y removing cores (often called plugs).  Top dressing (reintroducing soil to fill the holes) is achieved by leaving the plugs on the lawn and continuing to mow and water regularly.  By creating air space your turf will benefit from improved water and nutrient penetration to the root zone, resulting in a healthy root system to improve top growth.
     Aeration is a short-term disruption that has long-term benefits for your lawn. It is a necessary practice integral to the long-term health and beauty of your lawn.