Most homes have multiple valves: main incoming, bathroom-specific, kitchen, geyser, washing machine, etc. In a crisis—like a burst pipe or overflowing toilet—you don’t have time to play guessing games with every knob in the house.
While a plumber is there for regular work, asking them to show and label key valves (even with a marker or small tag) is smart. Write “Kitchen sink,” “Main,” “Geyser,” etc.
If something goes wrong later, you or any family member can shut off the right source quickly without panicking. It turns a confusing tangle of metal into a clear control panel.