Apple Motion 4 - Manual (Page 428)

For example, if you apply the Random Motion behavior to a shape, that shape might
weave around onscreen with a completely random animation path similar to the following:
Random animation path
If you turn the Random Motion behavior off temporarily and create an animation path
using keyframes, you can create a completely predictable and smooth movement.
Keyframed animation
path
You can combine the two by turning the Random Motion behavior back on, with the end
result being an animation path that follows the general direction you want, but that has
enough random variation in it to make it interesting.
Random animation path
combined with the
keyframed animation
path
While this example shows how you can combine behaviors and keyframes to create
animation paths, you can combine behaviors and keyframes for any parameter.
428 Chapter 9 Using Behaviors