Have you ever thought of yourself as a grass farmer? I often think I do what they do, just on a smaller scale. You'll notice in the Spring, farmers will till and prep the soil to create a light airy soil for planting. They have this benefit because they typically plant an annual crop that will be harvested in the Fall. Grass farmers don't have this option, because we don't want to re seed the lawn every year. Aeration can give you some of the benefits of tilling the soil without having to re-plant. Soils in the Treasure Valley usually contain high levels of clay. Over time mowing, foot traffic and kids play, will compact the clay and make it difficult for air, water and fertilizer to penetrate down to the roots. All of these are essential for healthy grass. Aerating removes small cores of soil, loosening soils and alleviating compaction. Air, water, and nutrients can now penetrate to roots where it can be absorbed by the grass. Our soils also have good bacteria that require air flow to break down the thatch layer, and boost the soils nutrients, organic matter and water retaining potential. Don't expect me to explain this any deeper than I just did.
Aerating also helps prevent water pooling in low spots (creating swamps) and running off high spots (creating dry spots) when you irrigate. Allowing all areas of your grass time to absorb every irrigation cycle more efficiently. Yearly aeration is highly recommended!