Magnus carlsens word


Btw - I think the focus on fast development and "tempo-winning-moves" in the openening are very applicable to any player being serious about chess. Since this part of the game lay the foundation of the rest of the game its importance cannot be understated. Of course one should also learn how to take advantage of a lead in development.
In a game with his Play Magnus app, Carlsen commented that "He is doing something very foolish..taking up pieces without finishing development" (not exactly maybe) . There was a undefended pawn near the centre in the opening and to me it looked as if I really should take it. so, as I have not heard something similar in opening guides for beginners and intermediates, my question is how applicable is that comment (especially for lower level players)?