How many or what % (however you want to state it) of deer that you've killed were the direct result of
1. Ranging the deer itself
2. Ranging objects once you got in stand
3. Guessing the yardage and being correct(not ranged at all)
4. The deer was close enough the range didn't matter.

Now how many deer do you feel you missed as a direct result if not using or having a rangefinder?