The Competition Scratch Score is intended to be an adjustment for the weather and course conditions. Provided most of the players in the field have correct handicaps to start with, then you would expect a greater percentage of the field to make buffer on a benign day than on a difficult windy day. Scoring a nett 2 or 3 over SSS on a difficult day may be just as good as being 2 or 3 under on an easy day. Cat-4 golfers are generally poorer than Cat-1s in terms of nett scores, but have a wider buffer zone. Seems fair enough to me!