Low repetition work (in the 1-5 rep range) provides an extremely unique adaptation. To overcome the weight, your body must recruit as many motor units as possible. This will cause your nervous system to become more efficient at this process. Over time, you will learn to lift the heavier weight with all (or close to as possible) of your motor units in one rep. Powerlifters are extremely strong for this reason. They can make all the their motor units fire at once!