Free bet is useless. Even if you win, you're unable to withdraw the winning proceeds.
Free bets are not useless and they can be withdrawn. It's not easy, you need a bit of luck and sports knowledge, but it happens. I remember when FortuneJack introduced eSports on their site. They offered me a 0.001 BTC free bet on eSports to test it out. I placed a bet, won it, reinvested the winnings a few times, and managed to withdraw in the end. This was at a time when FortuneJack had a minimum withdrawal limit of 0.004 BTC.
^ That could be the consequences that you may encounter in some gambling casino, you cant withdraw your small winning because there is a minimum withdrawal but I have an idea, it is possible that I can still withdraw my balance under the minimum withdrawal? For example, I have 0.003 BTC there but in order to reach the minimum amount of withdrawal, I will deposit 0.001 BTC so that I will be able to reach the minimum amount of withdrawal. Do you think this is possible?