A concrete example will help to explain things further:
I initiate a payout today on a gs containing:
Capital C : R10,000 (of which R1000 is the total interest to date)
Interest rate x% : 6
After 10 days the normal additional interest earned would be
10,000*(6/100)/12*(10/30) (close enough approximation)
= R17 ( rounded off)
So the total interest earned in gs up till payout date is I = R1,000 + R16.70 = R1,017
But the additional bonus interest is calculated as : I*((x +1)/x)=I*(7/6)=R1,187 ( rounded off) - R1,017
= R170
So total payout will be R10,000 + R170 = R10,170 ( vs an immediate payout of R10,000).
On a large 100K ish gs that's been accruing for a while that amount could thus be fairly substantial if you look at the numbers from example above.