I get the feeling that it is fashionable to spend a lot of time explaining why you do things to players. TELLING players to stand in position X rather than position Y is old fashioned! Instead, let's involve them in the learning process! Sometimes, the players can come up with better solutions on their own!
*italics = sarcasm*
Especially at the youngest ages, I've found explanations and justifications to be at best, superfluous, and at worst, a waste of time. If a coach knows what they're doing, the 'why' should become readily apparent either in training or in games. Even in situations where I do talk to players at length about why we approach the game a certain way, it's NEVER the first step in the process. In the lower-level club environment I work in, spending, say, 1 5 minutes each practice just speaking with players means I'm using nearly 10% (30 minutes from 3 hours) of training. With 9-10 year old boys, in my experience, speaking longer than 30 seconds is a no-no!
Instead, I focus on HOW I want my players to do something. For instance, a pass being a 'laser', vs. a 'rocket' is an important distinction in my teams. If I've done my homework, and I truly understand how a given tactic will play out, then the players should have success with it. Once they have a basic understanding, I can start revealing to them, in the proper context, the 'why'.