It is recommended that you shut off and turn on your supply line valves at least once a year. The reason is to keep them in working order in case an emergency should occur and the faucets or toilets need to have the water shut off. These valves can be found under the kitchen sink, vanity or toilet. I, like most people, did not put much importance on this project until just the other day. I decided to shut off and turn on each valve in my home. The results will surprise you as much as me; 2 valves did not work and where replaced and two supply lines from the valves to the toilets where leaking and causing wood rot on the baseboard. All said, probably a real good idea to perform this exercise.