A boat without any rocker placed on the same floor will touch the floor over most of its length. It'll be difficult to turn but easy to paddle straight. Tracking is more important than turning ability in touring and in sea kayaks. To strike a balance between tracking and turning most sea kayaks are designed with a small amount, one to three inches, of rocker. Longer boats, boats with vee-shaped hulls, and boats with very fine ends can have more rocker without compromising tracking.
Rocker improves a boat's handling in waves.
In heavy winds and seas rudders are invaluable. They are also useful in doubles and in heavily loaded singles. However, any kayak that must rely on a rudder to handle properly is unsafe. Rudders and skegs shouldn't be used as a remedy for poorly designed hull. A movable skeg can also be used to balance a boat in rough conditions.