One is a creation expression that makes use of random numbers in a few places for custom attributes that are used by a second runtime expression.
One simple example is that I set a random sprite rotation at creation time, and when I play back in Maya, it works fine. The sprites start at a random rotation, but stay that way through out playback.
But, when I batch render the sequence, it looks like every frame has a random rotation.
What am I doing wrong?