Tim wrote:
It is called a card protector. It is placed there to identify and protect the player's hole cards from an over zealous dealer who might accidently sweep them up and muck them when he is collecting other folded cards. It certainly isn't required but probably a good idea.

Yes, that certainly is one reason to protect your hand. The other reason is that when players muck their cards, most do so by tossing them toward the much. If they are the least bit upset the cards can, and do, land anywhere and everywhere. If a player throws their cards and they happen to land on your unprotected cards your hand is dead. You have no recourse. It is your responsibility to protect your hand.

I've seen the 8s throw their cards and kill the 3s hand.

If you don't take measures to protect your hand you, sooner or later, WILL have a hand killed in this manner.