Referral bonuses are just baits to win people over. In reality, its not what its actually presented as. The conditions are always vague until it gets to withdrawal, thats when you actually know whats at stake.
No, the referral bonus is intended for a gambling site to have more customers by having an affiliate share referral link and an affiliate will get number of benefits when a gambler registers using the link he or she has shared.
But the size of the bonus that can be obtained depends on how many accounts are registered with the link and also how many accounts make deposits on the gambling site.
If you think about it logically referral bonuses are equally beneficial for both parties.
Aside from the affiliate promotion that bonus depends on the number of registered users, some casinos actually offer an additional bonus where you can earn every amount spend of your referral. Meaning, ever deposit/bet of the referred user, a small percentage of it will directly go to your account. A type of bonus to gather more players/users.
Some of the gamblers make use of this method, using the bonus they get to be able to play even without depositing any amount of money. Trying their luck by the use of money from the referral bonus, and if they win, they got to withdraw their bonus + winnings.