most of the time free bets would mean you won’t receive anything even if you won which in that case you might already end up frustrated and might regret just not betting with money
This is only possible when you failed in your attempt to play a game, but if you won, then you're most likely going to win and earn as well, the only thing they ensure doing is to deduct from what you have earned the amount of money given to you as free bet back, then you take your own winning as profits, this is what is common to most of the gambling sites, except when specified that they are giving the kind that does not come in a form of free bet.