This process is used to remove thatch (non-decomposed organic matter) to allow for new growth generation and to alleviate compaction, allowing air flow into the sub layers of the green. You can pull a core or just punch a hole depending on the amount of thatch present. Different sizes of tines are used. From 3/8th of an inch to 5/8th. Sand is then used to fill the holes to help water infiltration and promote root growth.