Before revision: In the case of a missile or bomb, the (lack of the) arming plug prevents explosion before flight; in there case of a spacecraft or scientific sounding rocket, it might prevent premature firing of a hydrazine thruster system (hydrazine is extremely toxic) or block cryogenic or photographic film systems from operating before launch.
After revision: In the case of a missile or bomb, the (lack of the) arming plug prevents explosion before flight; in the case of a spacecraft or scientific sounding rocket, it might prevent premature firing of a hydrazine thruster system (hydrazine is extremely toxic) or block cryogenic or photographic film systems from operating before launch.