Time-Based Animation

An object animated based on time will move from point A to point B in the same amount of time regardless of the frame rate of the movie. The slower the frame rate, the farther the object moves each frame in order to maintain the same speed.

On the other hand, if the animation is based on the frame rate the object will always take the same number of frames to get from point A to point B. The slower the frame rate, the longer it will take because the distance moved each frame doesn't change.

You can see how time-based and frame-based animations act at varying movie frame rates in this demo. As frame rate slows, frame-based animation slows down and time-based gets "chunky".

Time-based animation is also known as "frame-rate independence".

Which Is Better?
Either method might be preferrable. It depends on what you want to happen if the run-time frame rate is slower, because of a slower computer, than what you set at authoring time. If you want the animation to slow down use frame-based; if you'd rather have the animation keep the same pace and get "chunky" use time-based.

You can mix the two as well. If you take a look at the code for the 3D Camera demo (modelRate script), you'll see that the animation is time-based until the frame rate drops below 25 frames/sec. Below that, the animation gets too chunky so it is slowed according to the frame rate.

Two Methods for Time-Based
Incremental animation and parametric animation each accomplish time-dependence in a different way.

In parametric animation, time-dependence is accomplished by using a time-based driver. See Driving the Parameter.

In incremental animation, time-dependence is accomplished by using an independent model rate. See Independent Model Rate.

The demos in those sections allow you to adjust the playback frame rate to see its effects on the animation.