Apple Motion 4 - Manual (Page 595)

Both the position and speed of your movement are recorded and applied to the position
keyframes for that object.
Keyframes close together
indicate slower
movement. Keyframes spaced far
apart indicate fast
movement.
You can further manipulate the path either by dragging individual keyframes, or
re-recording a new animation path for that object.
Keyframe Thinning
Due to the way keyframing works, if the playhead is at a new frame, and you set a new
value for a parameter, a keyframe is added. For animating while the project is playing,
this might mean setting a new keyframe on every single frame. This doesn’t create a
problem until you want to make a change to the curve.
In many cases, the curve created by your animation can be represented using fewer
keyframes. Often, this will provide a smoother rate of change and will enable you to take
advantage of the various interpolation methods such as Ease In and Ease Out.
595 Chapter 10 Keyframes and Curves