Very, very rarely I will tap to a lower DPI when in scope, but usually I just zoom in once more.
I've had this mouse for almost 2 years and have still not found a time to really use them [+ and -], though I can see reasons for it. I don't have a 90FOV-style 'zoom' button either, but I understand the idea. I just keep the DPI set to the max [1600].
I tried changing the buttons [+ and -] in SetPoint to key strokes , but I really have no extra commands I'd use and I find myself tapping the + button about every 45 seconds thoughtlessly, as I'm used to it not doing anything but offering a satisfying tactile silent-click to the pad of my aching, blood-thirsty, middle-finger.
I don't like changing the wrist-to-crosshairs movement ratio at any time. Just not my style of dance.