One of my pet peeves is when people hook up their regulators, turn on the air to check pressure, and either haven't fully turned it on or -- even worse -- turned it off while leaving the regulator hooked up so they won't lose any air prior to the start of the dive. Instead, you run the chance of losing your life.
The regulator-to-tank is a sealed system. It's not going to leak. If it is leaking, you have a different problem to solve before you start your dive.
If you absolutely insist on turning your air off, then also remove the regulator from the tank, so it won't look like everything is all set to go when your dive starts many minutes later, and you've forgotten that the air is off. Turning off the air, or not fully opening the valve, is simply stupid, puts your life at risk, and you're smarter than that.
So if this is something you're doing, don't send a message explaining how it's OK. Just stop doing it.
-- Ken Kurtis, Reef Seekers (Beverly Hills, CA)
www.Reefseekers.com