Scarification is a very important part of keeping your lawn in good condition because it removes excessive thatch.
What is thatch?
Thatch is a build up layer of surface and sub-surface dead grass, grass clippings and moss that can accumulate over many years. Too much thatch will cause deterioration in the quality of your lawn because it chokes the lawn and prevents nutrient, air and water from being efficient in the sward and rootzone. As a result the grass becomes thin, patchy and is prone to dying off quickly in times of drought. Removing this layer encourages fresh, more resilient grass growth.