The use of 4♣ and 4♦ bids as transfers to 4♥ and 4♠ respectively, either as opening bids or in response to 1NT/2NT. The transfer to 4♥ via 4♣ suggests a stronger hand than bidding 4♥ directly.
One benefit of playing that the transfer bid is two suits below the one shown is that it leaves room for partner to bid the in-between suit as a slam try.
Another is that partner is less likely to forget the bid is a transfer.
Playing South African Texas, the first hand would be a 4♠ opening and the second (stronger) hand a 4♦ opening.