Just a little something to hold your cards for you.
This might be the simplest feature you can get, but sometimes simple gets the job done. The cards holders are a little slot in the top of the table rail that you can set your cards in.
They're perfect for games where you need to reference your cards often, but aren't playing cards quickly. Like Catan, Hannabi, and card driven war games.
Card holder are also great for little kids who can't hold all the cards in their hand.
You'll probaby find a use for it in other games as well. For example, you can use it to show off which country you control in Imperial.