I might only add that from an operator’s point of view, you need to watch a couple of things:
1/ multiple accounts being opened by the same person which is something that has already been mentioned here before.
*Frankly, you wouldn’t believe what some people might be capable of in order to get a measly $10 freebie. Be it once or three hundred times, lol.*
2/ wagering requirements assigned to particular bonus which imho gets closest to what rmeeuwsen may have referred to as ‘bonus abuse’. Imagine the difference between the bonus wagering requirements varying as much as 1-100x and possible dent such promo can make to operator’s ROI if not set up in proper fashion.
Definitely not an easy task to set it up, especially if you want to stay away from ‘predatory’ bonus terms such 50-100x bonus+deposit amount.
3/ availability of bonuses on certain casino game types.
As it’s also been mentioned above, obviously you have different chance of winning when playing roulette, black jack, poker or slots. In reality some casino sites may only offer certain kind of bonuses for certain types of games, or at least offer different set of wagering requirements for different game types.
4/ ROI driven by players from particular countries.
Without giving any particular country names, we simply had to exclude players from certain countries from all no deposit bonus options at Slotland and Winaday, should we want to keep offering bonuses carrying mild wagering requirements.
Any more, anyone?