This is my very basic understanding of how nutrients work: If you work out a lot, you also need to eat a lot. If you work out a little you only need to eat a little. (And of course, you need a balanced diet with carbs, protein, fats etc)
My very basic understanding of protein powder is that powder is used by people who work out so much that they need to supplement their diet with protein powder, because it would be unreasonable for them to be able to eat so much protein without it.
If the two above are true, my question is: How do you know at what point your physical activity will require you to supplement your diet with protein powder (in other words, when is eating "normally" not enough)?