Coming at this from a slightly different perspective I've always been told that it's best to leave any vehicle with full tanks and over many years tinkering with cars, both fuel tanks I've had to replace were corroded from the inside out. Both vehicles were used by the previous owners as second cars and only part filled as they only did short runs.
Another thought occurs to me that bladder tanks lose flexibility if allowed to dry out, as you don't know how long it will be before the A/C is used again it would seem to be a sensible precaution to leave the tanks full.
Yet another thought occurs that the old natural rubber seals on riveted tanks would dry out if the tanks were not full.
So lots of reasons why it was good practice and may well still be. Perhaps another example of doing the right thing for the wrong reasons.
P S I don't have many cans in my shed overflowing with condensation. However I do have a whole buch that are really rusty!
