It is a necessity in my opinion. I had 8 out of 11 fish die in the matter of a couple of months from stress and disease. I found out by testing my tank with a volt meter that I had 46 volts of stray voltage in my tank. I believe that that contributed to their death. Now on the other hand, how much do you value your life? For instance, lets say you have a short in a piece of equipment and you stick your hand in the tank....depending on much stray voltage is in there you might feel nothing, only feel a little tingle or you may get knocked across the room or even die. The owner of my LFS was knocked clear across the room once. They cost about $17.00. A very small investment considering the cost of fish and the value of your own life. You have the facts now you have to decide.
