Thatch is the build up of moss, dead organic matter and sideways growing grass roots, creating an unhealthy blanket at the base of the plant which will choke the grass and stop sufficient moisture and nutrients to the soil.
Scarifying your lawn will mechanically remove this material letting your lawn breath and encourage new growth and a stronger lawn.
We don’t recommend a hard scarification in the springtime as this could damage the grass as it emerges from winter dormancy. A light clean through is best in spring with the autumn being the optimum time for this operation.