There are 4 valves on modern hoses.
Two at the hose ends and two on the guages.

When charging you open the hose end valves and the low pressure / blue valve on the guages.
Closing the high / red hose end traps high pressure gas in the red hose.

Opening the red / high valve on the guage let's the high pressure feed over to the low side.

I usually just close them all and hang the hoses because I feel that little bit is not a big deal. But its those little things like that that make a difference in so many things so it isn't a bad idea.