Adding a Friend lets gives you 5 more points to spend on your stats.
Removing a Friend removes 5 points from your highest stat for the first friend removed per day, 6 for the others.
You can have as many friends as (1/2* PlayerLevel + 1), with a minimum of 10 friends and maximum of 50 friends.
You can call your friends in a battle against a raid boss or quest boss in order to get help to defeat them.