As per the usual "removing stem after smoking" conversations, the point is that you not let the pipe dry with the stem removed, because the wood in the mortise is changing shape when the moisture level changes. Removing the stem for a minute or two after smoking will not destroy your pipe, but leaving the stem out for a day could allow the mortise to change shape enough to make it impossible to re-assemble. Though it's not entirely the same situation with a Spigot, you'll always be able to roughly fit the two pieces back together, I think it would still be best to always re-asseble the pipe after smoking (unless your leisure time is inturrupted by someone shooting at you).
What the Spigot or Military mount does do for the modern user is make it much easier to take apart and re-assemble, repeatedly, quickly and without much care. That tenon is going to be practically impossible to break from twisting and pulling in normal use. It may be true that a Military mount would still function if the mortise went out of round, but it would be a bit wobbly, and that's something that would dive me nuts.