This kind of bonus is normally associated with experienced players who like to deposit and to bet more than regular betters. Those adventurous players are usually called high rollers. Most of high-rollers are getting additional benefits from a casino for their active position.
In most of cases a highroller gets a certain percent of his deposit in a form of bonus money. This bonus is known as one of the biggest you can apply for.
High roller bonuses are mostly very generous - you have an opportunity to get tons of bonus cash. Nevertheless, you have to make an imposing deposit first. As far as there are huge sums on stake, we recommend you to read all the terms and conditions very carefully before accepting a bonus like this.