If one person stays at the end of CA - He gets a King of the Ring Emblem.
If 2-5 people stay at the end of CA - They each get a Saint of the Ring Emblem. (5 Saint Emblems = 1 King Emblem btw).
CA points are used for 2 things, Ranking and Horoscope quests. The top 5 players on CA ranking will have special effects if they have full Chaos set equipped. As for the Horoscope quests, you need a certain amount of CA points to finish them (Talking about Aries, Taurus, Gemini Quests.) - 50,100,150 respectively. Don't think there's more uses for CA points...