You will learn how to make something look like it goes from a stand still to moving fast, gradually.
Also, how to make something look like it is slowing down to a stop, gradually.
This is possible by either increasing or decreasing the spacing as you take pictures.
Why Is This Important?
The transition from fast to slow, or from slow to fast is everywhere in animation. Cars, super heroes, fish, parachutes and rockets are examples of things which go fast then slow, or slow then fast.
This is another very basic and necessary skill animators must master if an animation is successful.