In the real world, actions don’t start right away, the same principle applies in animation and is referred to as anticipation.
In an animation actions need to be set up in order to make them seem more realistic and to prepare the viewer for what the next action will be. The anticipation for an action can be seen as a character building up their energy for their next movement.
For example: Pongo moves his head back slightly before leaning over to lick Missis
Anticipation can also add humour to a movement, if the action that follows the build up isn’t what the viewer is expecting to happen: