Syedmurali,
That note only applies to the "fast-failover" feature that was introduced in 6.3 and is in 6.4. It is not mandatory, and you can continue to use VRRP and LMS-IP based failover. The fast-failover mechanism builds a tunnel to the primary controller and a backup controller. The enhancement allows more devices to form a tunnel using the fast-failover feature to a controller than would be allowed typically. This is to support N+1 redundancy.
For example, if a single controller is backing up 3 controllers, the access points on the three controllers will have a primary tunnel to those three controllers and a backup tunnel to the single controller (the +1). Those backup tunnels on the single controller can now temporarily exceed the number of access points that would be allowed on that controller to provide redundancy for the three controllers.