UR12 How to get sound only through headphones?

I have a UR12 and was wondering how to make the sound come only through the headphones output when plugged in, not the monitors ?(line output)
I can do this by turning off the monitors themselves but apparently that’s a bad thing…

Thank you

As the line out and headprone out share the same volume control I do not think there is much else to do, but then I can’t see why turning your monitors off would be a bad thing, go ahead and turn them off when you don´t want to use them.