Magnetic Declination, do we need to account for it?

Grid north on the map isn't the same as magnetic north as indicated by the compass needle. Do we need to take this into account when using map and compass? It depends where you are in the world. This video explains things from a UK point of view. Note at 2 mins 50 I say 25 seconds - I meant 25 minutes! (basically just less than half a degree)