The expressions simply check the velocity of your animations. If you move an objects motion ends abruptly (ie: you didn't easeIn @ 100%) the physics will kick in automatically.

Bake properties with detection of gaps and linear interpolation.

It allows you to select keys across multiple layers and
copy them back to a new location.

Simulating gravity turning on by a marker.

A very useful expression to automatically fade in and out based on the layers length.

Essentially, Inertial Bounce creates a bouncing motion of any parameter from one keyframe to the next, based on its velocity.

A great time-saving preset to "duck"(fade in/out) a music layer based on a voice over.
"Ducking - Audio Terms Explained - Process of automatic compression, eg when the announcer's voice signal causes the level of music to be attenuated."(from lp2cd.com)

These expressions save so much time, you might get home earlier tonight just by reading this.

Once you run the animation assistant for Exponential Scale, the keyframes are locked down and if you need to change the start or end values, you have to delete all the intermediate keframes and re-run the animation assistant. Here is a way to replicate the Exponential Scale via expression.

In this episode of Red Giant TV, Aharon Rabinowitz gives you some cool tips for working with numeric text, for things like video game scores and other digital readouts.