The instruction to remove the Armor when not in use may be because prolonged contact will damage the guitar.

It might, on the other hand, be because prolonged contact with the nitrocellulose finish on the guitar will damage the Armor.

Most likely, it's a mutual degradation of both, but in the absence of any comment on why the recommendation is made it's impossible to tell.

And does "in use" include when the guitar is in the case and needs to be protected from the tuners, capos, spare strings, pliers, wire cutters, tunning forks and other ȻЯȺP accessories people commonly carry around????

Modern merchandizing: "You don't need to know what it's for, just send us the money."

John (in slightly cynical mode)