It helps to equalize the pressure, some tanks have left hand twist, some right. I hate non-standard threads, for me it is always righty-tighty and I don't accept anything but. I hade to pay extra for an Nitrogen/C02 tank (CO2 tank, brand new, just marked as N and almost double the price), just to keep things straight.
With the gasket inside it does not take a lot of pressure to seal it but someone may have been on steroids when they set it. Take a good look at the threads and I'm sure you can loosen it, just be careful.
In Primary: Belgium Chimay clones.
In Secondary: Braggot, pale ale, end of the world white.
Conditioning: Mead, Cider, braggot, Belgium Wheat.
On Tap: Clones, Chimay Blue, Red, Porter, malted cider.
Bottles: Far, far, too many to list.