My wife is alergic to casein so dairy or beef is a no no, she also doesn't eat a lot and her diet was always carbs heavy, so after she decided to start weightlifting her diet had to change obviously to increase the amount of protein, which is a bit of a struggle if you are used to a certain type of diet your whole life and meat isn't cheap, so on days when she's not able to get enough from food, she'll have protein powder.
Supplements are just that, supplements. They exist to supplement your diet with the stuff you are missing. If you are not missing anything, then you have no need for supplements obviously, but if you are, they can be very helpful.
(I think we got quite offtopic
Anyway this was my last post for the day, so no more derailing. )