Safari Books Online is a digital library providing on-demand subscription access to thousands of learning resources.
The most noticeable visual difference between a simple show and a more polished show is motion. For something to move, it needs time to do it. Timing is naturally tied to motion. One cannot exist without the other.
Timing goes one step further than controlling the speed of motion. It also crosses over into synchronization with the beats and flow of the sound behind a slide show. Some simple audio discussion is covered here as well.