If you add something, say an effect, to a video track, then the objects to the right do not move; but if you then delete that same thing, the objects to the right do move (to the left).
If I had my druthers, the two actions would be symmetrical: "adding" would be an insertion of time, "removing" would be a deletion of time.
Actually, I'd like to be able to "freeze time" on a track so that you could add and delete things without having everything else slide around.
Better yet, you should be given the option of "inserting" or "overwriting" when you add, and similar options when you remove an object. Jerry Schwartz