A freeplay voucher is not the same as cash. If you put 5 $100 vouchers in and play $1 DDB for example, you play 100 hands and cash out. Now let's say that amount cashed out is $450. Had you done the exact same with cash and had the exact same hands, you'd have LOST $50. And if with the FP you cash out $550, you profit $550. With cash, you only profit $50. See the difference?