By default, an Absolute layer overwrites the previous layer's animation with a new animation. This means that, with two Absolute layers on the stack, only the second layer has any effect. The Absolute layer is the basic animation layer type that you work on most of the time.
The Relative Local layer is additive and local to preceding layers in the layer stack. Sometimes referred to as an adjustment layer, the Relative Local type is for editing the pose of your character, or applying adjustments to your animation. It applies its effect on top of the result of the previous layer. The effect of the Relative Local layer is always affected by the previous layer in the layer stack.
For example, if you apply a rotation offset on the X axis on a relative local layer, then as the animation of the previous layer moves and rotate the head, the head will always be rotated according to its own local axes. To visualize the way this layer works, suppose you have two objects linked together in 3ds Max Design. The Relative Local layer has the same effect as the child object. If you rotate the parent, the child moves in a circle around the parent. The child’s offset is always in the coordinate space of the parent, which is how the Relative Local layer works.
Sometimes referred to as an adjustment world layer, Relative World is useful for applying adjustments, always applies its adjustments in world space. That is, it ignores the results of the previous layers and always apply its effects the same way.
For example, Relative World is useful for editing the exact location of a foot plant during a walk sequence. If you used a Relative Local layer to adjust the position of a foot plant and then later rotated the foot slightly on the Absolute layer, then the foot location would change because the Relative Local offset would be rotated also. In such a situation, it would be more effective to use a Relative World layer.
The best way to learn which type of layer to use in a particular situation is by experimenting. In some cases a local space adjustment is suitable, while others are best suited to a world space adjustment. Learning these layering tools by working with them will allow you to make the most of the layering tools in CAT.