The Rotation controller is a component of the Transform controller. Rotation is a data type that can use most of the standard controllers such as TCB, Linear, and Noise.
Rotations in 3D are very complex. Even the standard controller types behave differently when used for rotation. The most common way of calculating rotations in 3D animation uses four components to define rotation about an arbitrary axis. This is the quaternion method.
Use the when you want individual function curve control for each axis of rotation. Euler XYZ is a compound controller that combines separate, single-value float controllers to specify an angle of rotation about each of the X, Y, and Z axes. Euler XYZ Rotation is the default controller applied to all objects.
Euler angles are well suited for animating mechanical rotations. They can also be a good choice for an object in an inverse kinematics chain because IK Rotational joints are defined as Euler angles. X, Y, and Z function curves displayed by this controller in Track View represent rotations in "world" or "parent" space which is the rotation system used by most 3D animation packages.
Customers upgrading from earlier versions of 3ds Max might find some difficulty in adapting to using Euler XYZ rotation controllers. If you find yourself experiencing unexpected rotation behavior, this might be the reason. Reassign TCB rotation as the default rotation controller and you will be able to regain your customary workflow.