Grass plants are stimulated to produce new shoots and roots that “fill up” the holes in the lawn and increase the density of the turf. Turfgrass stress due to compacted soils will weaken the grass plants over zoysia grass time, making them less able to compete with weeds and slow to recuperate from injury. Be sure to not confuse a compacted soil with an inherently poorly drained soil, although both can occur simultaneously.
The earthen plugs that are deposited on the lawn after each successive plunge actually benefit the lawn. They also contain microorganisms that help decompose any layers of thatch that are present. The simplest and cheapest way to aerify a small lawn is with a spading fork. Push the tines into the soil as far as you can and rock the fork back and forth to enlarge the holes. This movement will loosen up the soil and make room for new grass roots. One limitation of using a spading fork is that as you are making a hole, you are also forcing soil particles around the hole closer together, causing more compaction.
This method is also rather labor-intensive for treating large areas. While removing cores of soil, the spoons or tines also sever the roots, rhizomes, and stolons.