Apple Motion 4 - Manual (Page 274)

The project shown in the following image contains a particle system. Notice that the
animated particles, although not visible once they move off the Canvas, make the group
containing them very large.
Default size of a group
containing particles
Particles bounding box
You can crop the size of a group that contains growing objects using the Fixed Resolution
checkbox in the Group tab of the Inspector.
Group with Fixed Resolution
turned on
If your project contains animated objects that move or expand beyond the edges of the
Canvas and you don’t activate the Fixed Resolution checkbox, your computer processing
time may increase.
Note: The Group tab of the Inspector (which contains the Fixed Resolution parameter)
is only accessible when a group is selected in the project.
When the Fixed Resolution checkbox is selected, objects that are in the group but outside
of the Canvas are cropped to the size of the group defined in the parameter.
274 Chapter 6 Creating and Managing Projects