Since handicaps are calculated using .96 of the differentials for your best 10 rounds it favors the low handicapper over a high handicapped player assuming both handicaps are fair. Let me explain with a demonstration:
Bill's best differentials average out to 5. Using the USGA prescribed method of calculating a handicap, his handicap would be 4.8 because 5 x .96 = 4.8. His handicap is only .2 strokes better than what his differentials actually are.
Bill's friend, Paul, has his best differentials average out to 20. His handicap would be a 19.2 because 20 x .96 = 19.2. This means Paul is getting .6 extra strokes taken from his differential than Bill (remember, Bill only lost .2 of his differential on his handicap). Paul effectively will lose 1 stroke that he would otherwise be entitled to when playing against Bill because of the so-called "Bonus for Excellence" that is built into the handicap system in the form of the .96 multiplier of your differentials.
Is this one stroke meaningful? You tell me, but it's definitely a stroke that Paul will lose if Bill is any good at haggling handicaps on the first tee (Bill's best strategy would be to suggest that they round their handicaps to the nearest full number for "simplicity's sake").
Your talking index but when the index is put against the slope rating the higher capper will get more strokes, when getting into + indexes they go the other way +3.4 will be at +4 hdcp.