Since English is not my mother tongue, I will explain better and faster with movies, than with 100 lines here.
So, I have attached two movies.
Movie 'appearance of parts during presentation.avi' is showing, how three parts are appearing with this Appearance option.
And if I would want to have one part hidden during the whole animation, I would set the appearance to 0% and move the timeline for this part to the end of the presentation. So, everything will be animated first and only then, at the end of animation (let's say frame 100), the hidden parts will be shown. So, if I then record a movie, I will save it from frame 1 to frame 99. Frame 100 will not be included in the movie, so the parts will be hidden all the time.
Movie 'turn on-off parts during animation.avi' is showing, how I can click on parts in pathfinder during the animation. And thus turn off/on the parts.
Hope this helps.