When you explain the reasons behind why something is done a particular way, it aids in the learning for the individual you are teaching.
This is as it gives them more context and information to help them to understand what and why they are doing in that way.
I have found it the case in one of my past jobs where I worked as a swim teacher. In the beginning, I would teach by example and demonstrating the exact movement, positioning and style of each swimming technique. At times, there were some children who were able to pick it up from just that, that is, from seeing and then doing - but not everyone learns like that.
What I found even more useful to them (for those children who had were able to understand me then - directly or through analogies and examples) was that when I taught them the technique and then the reasoning behind it they were able to have the insight they needed to do it. As this helps them to think about the technique more and to tailor to their own needs as they understand what a particular stroke may be aiming to achieve. They may even do it better and show me a better way of doing it.
Looking back over my earlier years, I have found that knowing the reasoning behind things has personally aided in my learning. So the next time you are teaching or showing someone something, don't just show or tell them how it's done, tell them why as well. That way they may learn it that little bit more better - or even teach you a thing or two!