Tactics is the study of shapes, distances, angles, functions, formations, styles of play and so on. It is the X's and O's of pregame instructions, half time corrections and post game analysis. It is often presented as patterns or principles of play. It can be viewed as "what we will do" in the game.
Insight is different. It is more about the effect that tactics have on the game. It involves understanding the benefits or limitations of the tactical decisions. "When you play wide the defender has to choose between marking you and covering the center. If he covers the center, you get the pass. If he marks you, your teammate can dribble through the middle. Playing wide is the tactical concept, creating space. Seeing the dilemma that the defender has is insight. Too often players are told what to do without learning why they should do it. They never appreciate the "big picture" benefits of the ideas. This results in robotic play and a clichéd understanding of soccer problems.
An example. During a practice stop the game and ask a player why he chose to make a particular pass. Chances are the answer will be 1) I don't know or 2) He was open. If the answer is 1, that's a problem. If it's 2 ask them "so what if he's open?" The next answer you get will show a level of insight. Being "open" isn't a very good reason for a pass. One reason that he's open is that he doesn't have the ball. Now that he does is the team in a better situation? How did that pass contribute to the teams efforts to win the game? A better answer might be "I was under pressure and had to keep possession" or "he was facing the field and could make a better decision." These answers show an appreciation of why a decision (the pass) was made.
Insight involves value judgments and a grasp of the correct moment. It is an awareness of team mates and opponents strengths and weaknesses. It is ability to choose the correct answer to solve the problem in a team efficient manner. When players understand more complex problems and how to solve them they are said to "have insight or vision." However, the appreciation of when, the correct moment, cannot be overstated.
There is also the element of predicting. What will happen when; what happens if; how will he react when and so on. This is one element that great players, ones that can "read the game," and are always "two steps ahead," possess. They can accurately forecast future events using numerous probabilities. This is why asking questions, instead of giving information, is so important in player development. When asked, a player has to think and supply an answer. When told he simply accepts what is said and he may or may not have to think about it. The process of problem solving is given a short cut. They don't have to "figure it out," just supply a knee jerk response or wait until the coach tells them what to do.
Youth players can be taught that there is a difference between what is possible and what is probable. This is lacking in most because they are not mature enough to grasp percentages. Their answers tend to be the simplest one. A player can think that trying to dribble the ball the length of the field and score is a good idea because he did it once. He forgets the 55 times that he lost the ball. One out of 56 are not very good odds, but, it is possible, it's just not probable.
Teaching tactics without insight is like learning to steer a car without learning that it helps you to avoid collisions. It results in a shallow appreciation of solutions. Coaching to gain insight (understanding the effects, predicting future events) naturally brings players to tactical and technical solutions while the opposite is not necessarily true. When players understand why they need to find a better way to do things they tend to figure out the how tos on their own and this puts a greater value on their answer.