Soil compaction will keep your lawn from being as healthy as possible, and correcting the soil compaction will allow air, water, and fertilizer easier access to the root zone. An aeration will pull out cores of your soil to help correct soil compaction, stimulate root growth, and allow air and nutrients into the soil.
A core aeration will also allow for better penetration of water and fertilizer into the soil, and results in better water management. Aerations should be done once per year and can be done any time of year when there is adequate moisture in the soil.