Lawn scarify or scarification is a form of mechanical raking. We scarify lawns primarily to remove dead moss and thatch eradication. Moss can easily be removed but there is normally a physical reason why the moss is there in the first place. Thatch is a layer of dead and living organic matter that occurs if it is not raked out or cored out. Thatch has a spongy consistency and, like sponge, soaks up a large amount of water not allowing nutrients and air to move through the soil profile, thus drowning the plants.
Regular scarifying of a lawn is great practice, regular raking out dead moss and any broad-leaved weeds just leaves the surface of the lawn cleaner and allows new grass plants to thrive. You would be amazed by the amount of organic matter that can be removed by scarifying a lawn. Always scarify in 2 directions and vary the depth, shallower first. typically set the depth to 5mm below the surface.
Photo shows the lines created by the scarifier and the holes created by the spiker during our standard renovation program.