Reply to The concept of using 4Decks

Hey guys, I'm pretty new to spinning but my biggest thing right now is using all 4 decks. I have a Traktor control s4 but I'm pretty much only using 2 decks when twitching to a new song. What is the concept of using the extra 2 decks... playing loops behind the songs currently playing? or what? I get you could use the sample racks and a use them that way, but I don't understand the whole concept behind using all 4 decks simultaneously... can anyone help explain?