Many casinos offer free bonuses with no wagering requirements at all. But as a rule, they have to put some limit on how much you are allowed to withdraw before you deposit money at the casino.
Let's take an example where you get 10 free spins just by signing up. Then there is usually a limit on winnings of 150€ and up to 200€, perhaps in some cases lower limits as well. But this restriction applies only if you have never made a deposit to this casino before. The minimum deposit at the casino today is around 10€, so wouldn't it be worth making a small deposit in case you land big winnings on the reels?
In some cases, you may also have a cap on how much you can be allowed to withdraw on free spins, even if you make a deposit. So it is wise to look at such terms before you start, but still, you should rather see this as an opportunity to get away with some winnings with no obligation to continue to make a deposit, rather than hunt for the big jackpots with free bonuses.