I'm using a "cheap" one (I think it was like 80 EUR), and it's mind blowing how convenient it is despite its small size. Now trying to use a physical whiteboard for brainstorming, feels the same way as trying to use pen and paper for programming: technically doable, but I curse internally because the inconvenience.
Just being able to select stuff and move it around, or undo with a quick Ctrl+Z, or rotate things, makes all the difference.
Sure, I love using a paper notebook for my notes, and the feel of writing with a pencil on paper is really nice; and I would use it for drawing quick stuff if I don't have anything else at hand. But if I think I'm going to be erasing a lot, or that I will be doing the kind of stuff that is usually done with a whiteboard, a drawing tablet is (to me) a vastly superior option.