I do know that stay in Zoom in view is not good for SA, but since I don't have a large screen, it is useful to get a 3~5 seconds long scan by zoom in while moving as combat pace, just doing this can makes you exhaust. I don't have extra mouse key for Zoom in only as the "NUM+" Key.
Also I have a freetrack, using that can totaly ignore this issue, but it takes me a while to setup, sometimes I just want to jump in the game and start to play, so I not always use it, that makes me find out this problem.