I agree! This is exactly what I do too. It'll save on motor and cylinder wear as well.You don't have to leave it open, all you have to do is open it until the air coming out is not like a mist then close it back up. If you always drain all the air pressure out of your tank it is not a big deal to leave it open but I keep mine pressurized all the time to be ready to use it without having to wait the 6 min for it to pressurize.
So if you let it pump up to pressure, then cool down and crack the valve to shoot the water out you can leave the tank pressurized but w/ minimal moisture in it?
When I used the compressor in any way I wait overnight until the air in the tank cooled then drain the next day
I added a extension and ball valve the good thing is that it provide a little space for water to go to instead of sitting at the tank bottom. I used brass hardware so that is not going to rust either.