How many cat treats should you give your cat per day?

My roommate likes to give 15-20 at a time, 2 times per day. I've done a little research, and most people say 4-5 in a day. But these 2 cats aren't getting obese or anything. Is there anything else wrong with giving your cat too many treats? I just find it annoying how much they beg for these treats to the point where they're not even used as rewards anymore. It's just expected food for them, and they just beg until my roommate gives in and gives them 15-20 more treats. I know I shouldn't really care, but he's completely broke, will go without eating in a day, but will still go out and buy a bag of cat treats each day, usually a bag of the Purina Whisker Lickins'.