Powered aerators rapidly punch holes in the sod and remove plugs, which are deposited on the surface of the lawn. The benefits of aerating your lawn also include stimulating root growth by providing a more porous and easy to navigate soil texture. Lawn aerating is not always necessary annually on low thatch varieties of grass, but it cannot really hurt to increase the movement of water to the roots.
By reducing soil compaction, aeration also reduces water runoff and thatch buildup. If you’re not core aerating, then you’re probably not helping your lawn. Core aeration is when those little tube plugs are removed from the lawn. Some aeration practices just force a hole in the lawn without any removal; this jamming makes soil compaction worse. Thick, clay-like soil that easily traps water needs to be aerated more frequently.
Especially thick types of grass may also call for aerating more frequently. As a general rule, you shouldn’t need to aerate more than once a year at any time (“too much of a good thing” applies here, since you don’t want to damage your soil). More expensive aerating lawn tools, called coring machines, are also available.