Ah, but if your camera is on a tripod and your target is stationary and you are using manual focus, using the zoom on the display will allow you to get extra crispy focus. I shoot birds with a telephoto lens. First I set up a target in the expected flight path and focus on it using manual focus and the display zoomed all the way in. I then remove the target and wait for the action to begin.
Of course, depth of field on a 500mm lens on a 5100 at 10 ft is less than 3 inches so there are a lot of throw away pix. But when the flight path is just right, you can get some nice pix.
I also use the same technique with portraits. In that case, the subject's eye is the target. Same for still life's and macros.
Be sure to zoom back out to check your composition. It's a bit of a shock when expecting to get just the polllen of a flower and getting the whole flower. (Although my "Flying Hybiscus" was a rather pleasant shock)