NOS Bottle filling, freeze or don't freeze?

Question

Some refill shops say to leave my bottle so they can freeze it before they fill it. Some shops do not. Is this necessary, and why, or why not. If I freeze it myself do i freeze it with the valve open or closed, or does it matter?

Answer 1

(nitrous boils at -128 degrees F)
Some shops freeze the bottle so that when the nitrous is introduced into the bottle it has less of a chance to boil when they are filling it and it can be filled more rapidly.