Activate Anchor Transform in the Create Editable Motion Trails options to isolate the movement of a transform so you can see it in a local context, even in the middle of a walk cycle or a finished animation. This is useful when you need to isolate the action of a single transform relative to the movement of the rest of the rig.
Motion trails trace the object's motion through 3D space, but if you activate Anchor Transform, the motion trail illustrates the motion of the object as it appears from the camera's point-of-view.
For example, if a camera is following a character so that the character is always shown framed in the center of the screen, even if the character is moving a long distance in a lateral motion, the motion trail displays as a tight tangle in the center of the screen where the character is appearing. This is because, from the follow camera's perspective, there is very little motion.
Anchor Transform lets you sync an object to an animated camera to show the movement of an object relative to the camera. So when a camera is animated in a scene, even if the objects are not animated, the movement of the object in the "film-space" of the camera is displayed.
To use Anchor Transform to isolate animation
The Motion trail of the object from the camera's point-of-view appears when you play the animation.