prevents cable slap.
you'll know what this is when you hear the slapping on bumpy sections.
Not quite right. Their intended purpose is to fool you into thinking they're there to stop cable slap so that you reposition them before every ride because the useless rotten things have migrated to the end of the cable. They were specifically designed after a long lunch by a committee put together by Shimano to investigate new things to occupy obsessive compulsive riders.
Richard