Removing the strings and completely loosening the truss rod.

[superheavydeathmetal]

What would happen to a neck if I completely loosen the truss rod (assuming it is single-action, of course) and remove the strings?

Presumably, there would then be no tension on the neck whatsoever. Is that correct?

[LHBASSIST]

What would happen to a neck if I completely loosen the truss rod (assuming it is single-action, of course) and remove the strings?

Presumably, there would then be no tension on the neck whatsoever. Is that correct?

It really depends on the neck. I just did a neck repair on a Schecter Diamond series Deluxe 4 string bass. It had just broken. It was a totally clean break, and went together easily. The neck, with the rod left adjusted as it was, no longer under string tension, was backbowed to an extreme level. This is because of really below average strength billets used for the necks, and the really thin necks these manufacturers like to make now. Spongy, weak necks that almost completely rely on truss rod tension. I see all kinds of string tension related neck movement. The lower level Chinese/ Indonesian/ Korean instruments are most prone to this, instruments like this Schecter, Deans, cheaper Ibanez's well, you get the idea. Good quality instruments will likely bow back with the rod still under tension.
Theoretically, taking the strings off, and loosening the rod- will put the neck in a 'neutral' place- being subjected to neither string tension nor added tension from the truss rod. I do not think it would be harmful at all. Just remember to adjust it when you do put strings back on it...