Compacted soil prevents grass from establishing a healthy root system and keeps nutrients and water from reaching the roots.

In many yards, fertile topsoil may have been buried during excavation for the foundation, forcing grass to grow in dirt that is more compact, higher in clay content and not conducive to a healthy lawn.

Normal travel patterns and maintenance such as mowing will compact soil and damage lawns. Rain and watering also pack the soil, reducing large air spaces where roots readily grow. 

Aeration can restore movement and flow, allowing your grass to grow deeper roots and make better use of water and fertilizers.
An aerator pulls plugs out of your soil. This helps loosen compacted soil and allows air and water to reach the roots. This helps your roots grow more deeply and produce a stronger, more vigorous lawn for next spring. In turn, that better prepares the grass for the heat and stress of the summer months. By aerating in the late summer, you give your lawn a fall growing season and a spring growing season to deepen roots a prepare for next summer.