Used as an insult. If you say someone is ‘spare parts’ then you’re calling them useless, or they’re so poor at what they are doing that they might as well be doing nothing.
In a co-op video game, if there’s someone in your party that ends up doing jack shit for the team, then you’d say they are “spare parts.”
Player 1: Dude, player 3 got no absolutely no kills the entire round.
Player 2: I know, right? He just sat on his ass the whole game!
Player 1: Yup—he’s spare parts.
Phrase used by sadistic managers (particularly in IT) to describe any moment of spare time their employee(s) might have.
The implication is that the employee is like an old mainframe computer, and should be put to work for every second of the day or else corporate value is lost.
Boss: "Hey, Bob has some spare cycles, he can do these 29 extra tasks."
Bob: <grunts incoherently and shuffles closer to complete mental breakdown>