[Al Skierkiewicz]

Tristan,
The material used for the battery terminal is plastic as it is a very soft material being mostly lead. As such, the tightening of small hardware cause it to not only stretch and creep but also to "dish" in the process. As this occurs, the hardware does become loose requiring teams to tighten as needed. Any movement between terminals cause the wear I described above, again requiring adjustment of the hardware. Any rotational movement between the two terminals also causes the hardware to loosen. The addition of a star washer between the terminal surfaces prevents any movement between the terminals and therefore prevents both the wear and the loose hardware. While small changes in the deformity of the parts still occurs, the spring tension of the star washer facets keeps everything tight. By the time, the spring of the star washers can no longer hold the parts in alignment, the battery should have reached it's end of life (about 4 years maximum for most batteries.)
To restate, without the lock washer, the terminals will move, there is nothing to prevent it.