I think of a cog as only having one task it can do: go around to mesh with neighboring gears, but if the other gears are skipping or missing teeth, they can't step in. I don't think of people as being interchangeable, either, to extend the metaphor.

The image I like for teamwork is a circus trapeze. The troupe performs, catching each other, weaving a seamless spectacle. The audience is wowed, and the troupe knows they put on a good show.