When to turn on the water for my washing machine?
Most modern machines will self regulate the amount of water allowed to enter the washer. The typical washing machine is connected to the water supply by a hose. The hoses can fail with age. The most common use of a shut off valve like yours is to stop the flow of water when the machine is not in use. So you would open the valve allow the washing machine to run it's complete cycle. You would then close the valve to prevent flooding the apartment in the event the hose leaked while unattended.