Tom,
Nobody has mentioned the two that I have had experience with....
If you are going to leave the tank fitting bare, you best get a cap for it. Little crawly things love to go in there and make nests. When the remnants of those nests get into the regulator, there is A: Great Danger and B: Now way to salvage most regulators.
Second and interesting was an acquaintance left one tank home. This left the metal line that was supposed to be supported by the tank connection out dancing in the wind. Said line hardened and cracked. this was dangerous too, but at least the LP showed itself as soon as that tank was opened.
Matt