It's hard to prove with free money then we will have more wins in betting because on the basis we have a small chance and it might take a long time to be lucky.
So whatever it is I have never felt it with free money can be success like that which just deserves people will not be strong in doing tricks of this kind, which I know in gambling still need big capital to win it.
Would make no sense to throw away free money at your customers without making it hard to withdraw or turn it into a profit. The chances are the same though, no matter if the money has been deposited or given away. Casinos give free bonuses and bucks as a customer bait. Usually, the players start out by trying to multiply the bonus and end up actually depositing.