Some games are restricted, and you need to stay away from them when playing with bonus money. You are required to follow the maximum bet rule and never place higher-than-allowed bets.
This rule is most commonly used with no deposit bonuses, where we understand and tolerate its use, but we are against using the maximum conversion rule with deposit bonuses (at least some of them, depending on other bonus conditions). These are generally so high, that you are very likely to lose everything before you meet them, which is what casinos rely on to stay profitable.
Here are some examples of rules commonly associated with bonus play: