To be honest, I have signed up to many casinos but most of the casinos have separate terms and conditions to claim these free spin rewards and I have tried to fulfill those conditions by depositing in some cases but on the contrary the amount I deposited I have lost that amount. So that means that I have not been able to fund even a minimum of 1 dollar from here, what about the significant amount from free spins.
Free spins that require you to make deposits to be able to withdraw your winnings instead of asking you for a rollover are the worst and I would never be willing to claim such free spins because there is no point at all. If you are given free spins to try out a platform, you shouldn't be asked for a deposit for that if you manage to win something, a wagering requirement is good enough for that.
Moreover, so far I have not seen anyone on the forum or to my knowledge anyone winning significant amount of funds from free spins of any casino. I think free spin is a strategy to promote casinos, I won't say in all cases the casino wins in this strategy, in some cases very few people are lucky enough to win funds from free-spin and also fulfill their terms and conditions.
Of course, they use free spins as a marketing tactic to lure in gamblers and then get them hooked on the platform. Every single promotion, whether it is a bonus, free spins, a free bet, or anything else, they are all done to promote a platform and attract more customers. In most cases, it works very well, in some, it might not.