The strong side of the basketball court depends solely on where the ball is during that
possession. The side of the court where the ball is is the strong side and the other side where the ball is not is the weak side. This can change every possession or even changes within the same possession if the ball is reversed. So, the strong side travels with the ball wherever it goes the entire time the game is going on.
A common tactic from many offenses across basketball includes some sort of overload on the strong side. In other words, 3 or 4 players will be aligned on the strong side where the ball is stretching the defense to cover everyone on the court creating good scoring opportunities. Using the strong side and alignment on that side of the court can be quite beneficial to success especially when the one player on the weak side can make perimeter shots because a quick reversal turns into easy points.
The most important part of defense besides preventing points as much as possible is staying in front of offensive players. This usually makes the strong side the most important part of the court to guard at all times. Staying in front of ball handlers and in passing lanes on the strong side is important to maintaining good defense and forcing bad shots. So, defending the strong side whether in man or zone is very important to the defense as a whole and if the strong side is defended well, a team is very likely to win most of their games.