Is scarifying necessary?

As turf-grass grows it naturally develops thatch which is a tightly intermingled layer of living and dead stems, leaves and roots which accumulate between the grass and the soil underneath. One of the factors that reduces lawn speeds is excessive thatch and historically clubs have tried to combat this by aggressive scarification or verticutting. This approach can have unfortunate side effects, one of which is to create bare patches which are then invaded by annual meadow grass. 
The Sports Turf Research Institute has published a series of articles relating to “Disturbance Theory” which recommend a less aggressive approach to grass care. In fact the best method is to work with the biology of your surface and treat thatch as a nutrient. It is organic matter and therefore can be broken down by bacteria and micro-organisms into usable nutrient form. This method forms the basis of my biofeed nutrition programmes which encourage a biologically active root-zone.  
One example is Letchworth Croquet Club whose lawns have not been scarified at all in the last five years and do not require scarification this year. The measurable thatch layer has not increased during that period. This lack of aggression means that the root mass is stronger and healthier and the playing surface has improved as a result.
It is important to incorporate regular aeration in the programme so that life sustaining air and water reach the micro-organisms in the root zone.
If the thatch layer has become excessive, removal is necessary to allow water and nutrients to get down to the roots.  If it is allowed to build up it can form a thick layer and act rather like a sponge preventing water from penetrating the soil. Recently I took a plug sample from a lawn a few days after 2" of rain had fallen. It had a thick thatch layer which was sopping wet but the soil below was as dry as dust. Consequently the grass was rooting in the thatch layer which means that it had zero drought tolerance and much of it died during the summer heat wave. 
After the removal of excessive thatch I recommend regular light scarification with the blades set about 2mm above the soil surface which removes dead matter from the surface. Mowers such as the Allett Tournament mower incorporate a groomer reel in front of the cylinder. This counter rotates and flicks up dead material and stems into the cutting cylinder and reduces the production of thatch.

Scarifying at Guildford and Godalming Croquet Club

Allett Cutting blades, groomer and front roller