A scope having 100 MOA total elevation means from the very bottom of the rotations to the very top. You actually zero with a rifle and some fired rounds is going to be at least in the middle, possibly a little above it. Which means, after zeroing, you will have less than 100 MOA to adjust before hitting the top. If you have zero stop, it depends on the style of zero stop. Arkens have a zero stop that is good and lets you run to the top of the turret rotation.
Some Vortex scopes have a Rev Stop ring for zero stop and that allows 2 full rotations before stopping. Which can still be good, depending on what cant of rail you have on. For example, long range shooters and some long range hunters are often putting on a 20 MOA rail and zeroing at 200 yards, which gets back some the MOA or Mils that you may want.