There are basically two types of handpieces, air-driven and electric. Electric handpieces are much stronger than air-driven due to the fact that a motor is spinning the bur as opposed to air. This allows the doctor to remove decay at a faster pace. Another advantage is the electric handpiece sound is about 20% softer, minimizing that shrill dental whine people dislike.
As in all options, there are advantages and disadvantages of each. Dr Reider will always use the best tool for each specific situation.