Spacing is the hardest thing in the world to learn and put into a scene. With a scene with dialogue you need to emphasise to "favour" parts of the scene with emotions, timing and poses and this is all Spacing.You can also understand some of the importance of it if you look at your video reference, why are you putting more emphasis into part of it into instead of another part, why does that pose, that gesture feel more natural to you then another that you have recorded yourself doing. Animation is not the process of doing it is the process of feeling and asking why? why push key frame on frame 36? why get out my comfort zone and actually try to process what's actually going around me (actions/gestures, emotions) as I get up to when I go to bed? Clue: its about becoming a better animator.
One of my old teachers, Ian Lacey has put on his blog Animation Garden, about learning the concept of Spacing.
Overcoming hurdles for teaching and learning Spacing - Part1 and Part 2