Why store Variables in Animation Blueprint?

Hi there. In every Tutorial etc. I see that Variables for Velocity etc are stored additional in the Animation Blueprint.
My question is simply: why?
Why not storing the Character/Pawn only and access the variables directly?
Isn’t this a waste of space and a performance hit if you need a lot of variables from the pawn?
Most variables can be calculated on the fly (Direction for a blendspace for example)

The only Problem I see here is, that you can’t have a Preview (because References are by default null).