Many power tools and machines can be used with either hand, but some are simply made for right-handed people. Sometimes this means that a power switch is farther away from your thumb than you would like and a few tools can wreak havoc if used with the wrong hand, according to an article in Baylor University Medical Center Proceedings.
Circular saws are perfect examples—they are typically designed so that the spinning blade is positioned on the outside of the hand you are using to grip the tool—away from the hand holding the material you are cutting. Therefore a circular saw built for a right-handed person is difficult and unsafe to use with the left hand.
Fortunately, left-handed circular saws and other power tools are available. On a left-handed circular saw, the blade sits to the left of the handle, so it is further away from your right hand, which you are using to hold the wood, sheet rock, or other cutting material.