Microgaming developed the clearplay bonus system in order to make sure that the casino’s incentive for offering bonuses was not lost.
In other words, if players were allowed to withdraw their bonus the minute they received it, the purpose the bonus (to encourage new players to the casino to play with real money) would be defeated. The clearplay bonus system also goes by the names of eZ or Flexi bonus system and was developed quite some time ago in 2006, however, it has undergone drastic modifications since then.
Most Microgaming casinos implement this system which splits your casino account into two sections: one for a cash balance and the other being your bonus balance. As you wager, your bonus balance will be incrementally transferred over to the cash balance. It used to be that you could withdraw your winnings at any point. However, now most impose a play through requirement.
Nowadays you need to complete the wagering requirement before you can withdraw even a portion of your balance. In case where you can withdraw before the wagering requirement has been met, you will forfeit the balance in your bonus section of your account.