This is something that every gambling site is only too happy to ask of its players these days. What I don't think is correct is that gambling sites abuse this mechanism to withhold payouts as long as possible. Only when a player has won a lot of money and wants to pay out, sites come up with this KYC procedure. Very unfortunate, because that way the general image of the gambling site will not improve in general. It will also have a lot to do with which country you obtained your gambling license through.
I am sure only shady xasinoa will want to use kyc to nail their players for winning a big amount and it sound irritating to hear such complaints coming from some playees how the casino suddenly demand for kyc documents immediately their place for withdrawal,, and if the mount is smaller than the limit for non-kyc withdrawal which os some time set as $5000.
So any amount below this amount can be withdrawn without KYC verification., so at that it becomes mandatory to take note of the balance and amount you want to withdraw in such an account.