Upon reading Bruce Lee's writings, it is clear that he was a big proponent of placing the strong side of our body forward. Why is this? One of the main reasons is because we want to put our dominant hand and dominant leg closer to our opponent. There are a few reasons for this.
The first one, an arguably most important, is interception. The closer my strong hand is to my opponent, the quicker it will be able to reach its target. If my opponent is lunging at me, then my strong hand and strong leg being closer to him will allow my strike to land as early as possible. Effectively stopping the oncoming attack.
The second reason. If I put my strong side forward it means my weak side is back. By putting my weak side back it gains all the power from the torquing motion of my hips effectively making my weak side more powerful.