It's all about the body mechanics when we talk about exercise. Whether we are moving an external load, or even just our bodyweight, keeping the ideal positions based on our own physical characteristics and constraints is key to getting the most benefits from the exercise we are performing.
Whether you are a Crossfitter, a bodybuilder, a weightlifter or a runner, every movement we do involves us aiming to hit certain positions to be as mechanically effective and efficient as possible. This is also why most of our sporting movements have been broken down in various phases for easier recognition and understanding.
Once we are able to hit these positions, we are in a better situation to be effective in the movement. Putting it in context of weightlifting and from all the reading I do on the topic, by our knees moving into position for the double knee bend, we prepare ourselves to effectively use the knee and hip extensors for force development in the second pull. If we do not properly get into that position, force can still be developed but probably in the wrong direction or at the wrong time or using the wrong mechanical lever.
However, with that, there comes the tendency to break down the movement too much. It is alright to break a movement down to learn the needed positions. But in the end, you want to make sure the movement is completed as a whole and not in segments. After you learn the various positions, you want to make sure you get fluidity of the movement. Transiting from one phase to another is actually key to make the whole movement effective and efficient. You can see this happening with many drills available to enhance various parts of the movement. Yes these drills reinforce movement in the various phases. But eventually, the overall movement should be kept whole. The drills supplement your learning of the movement but the full movement should still be done to ensure that the whole puzzle can be pieced together.
Though I may not have as much experience in coaching and teaching, but I have recently began using the weightlifting movements alot more in the training of my clients now. Teaching them the snatch and the clean involves alot of maintaining the positions. Adopting a top-down or bottom-up approach which reinforces the various phases have helped them learn the movement well. But no matter what, I always finish off with the entire movement so either the snatch or the clean to ensure that the entire movement is reinforced and not just a single part of the movement.
So for today, remember that breaking down a movement to different parts is a good thing but you also need to ensure fluidity of the whole movement to ensure that the right movement pattern is learnt.