It depends on the image if you need to apply sharping. I don't use it often and only do so after checking the image at about 200%. After applying the sharping check the image again at about 200% and pay attention to areas of contrast, as too much sharping will show up here first. Increasing the size of the image to A2 shouldn't make any difference to the sharping applied. Larger images should be viewed where you can view the whole image at once.
