Have you ever noticed that experts make extremely hard tasks look relatively easy? That's because they have learned how to consistently and accurately achieve the zero point - the minimum amount of effort or energy needed to successfully execute a specific function.
When we first learn something, we often over-exaggerate the energy required to be successful. Since most successes are often interpreted as a range (for example, there are many ways you could park a car into a parking space without hitting neighboring cars), we tend to choose an effort level that is safely and conservatively in-between two points we know will be unsuccessful (e.g. parking perfectly in the middle between two cars).
Think of effort as a line: on one end of the line, there is too little effort to perform the desired task, on the other end, there is too much, resulting in wasted effort. There will invariably be a range of effort levels that will all produce successful results. However, some of those effort levels will be two, three, or even four times more strenuous than the minimum amount of effort required to produce a successful result.
So, when your teacher tells you that you need to raise your right shoulder in order to access a different string, you are most likely going to figure out how much that shoulder needs to move in order to be exactly in-between both strings. However, you may be surprised to learn that an expert may move just enough to narrowly dodge the previous string, while playing the new string at an angle extremely close to the old string!
Remember, our goal during practice is to discover ways to increase our output while reducing our input. Another way to say that is that we want to produce better results by using less effort! If we no longer have to overwork in order to produce a specific result, then we can use the energy we save towards the myriad other details in a given piece.
Perhaps the most important reason for finding the zero point is to increase speed. Without having to waste energy going from one extreme to the other, we literally save the time we would have used being inefficient with our movements and transfer them into an increase in execution time. If you've ever wanted to play faster, simply find the zero point!