Timing is what allowed the spacing in the animation to move to the according speed that it should be moving. Adding the correct timing with correct spacing will make the animation move in a realistic manner. If you mess up either the timing, spacing or possibly both, that will cause the animation to look a little less realistic than it should be. Timing and spacing is the defining factor that creates a good looking animation. For example, if I would not have focused on the timing of the pendulum, it would not look like it was slightly slowing down. If I didn't focus on the spacing of the pendulum and rotate it the same distance each time, it would never stop. Same with the timing, If I did not focus on the timing, it may look like the pendulum is falling slower faster through each swing.
