.invalidate()

Clears any initialization data (like recorded starting/ending values) which can be useful if, for example, you want to restart a tween without reverting to any previously recorded starting values. When you invalidate() an animation, it will be re-initialized the next time it renders and its varsobject will be re-parsed. The timing of the animation (duration, startTime, delay) will not be affected.

For example, let's say element.x is 0 and then you TweenMax.to(element, 2, {x:"+=100"}), it will animate from 0 to 100 over the course of 2 seconds. If you restart() that tween, it'll do exactly the same (animate from 0 to 100). But let's say after that tween runs once, you'd like to flush the starting/ending values that were recorded internally so that  x animates to 100 more than where it is NOW (which in this example would be 100). If we now call invalidate() on that tween, it'll re-parse the starting/ending values on the next render, thus causing it to animate x from 100 to 200. 

When you invalidate a TimelineLite/TimelineMax, it automatically invalidates all of its children.

Below is an informal video explaining how invalidate works on a single tween.

Demo