This is largely incorrect. That bypass is occasionally used for what you describe but more often than not it is used as a way to do what's called a "blow out," by allowing guests to leave the park in a more expedited fashion, especially during parades, fireworks or at other peak times when Main Street may be clogged with people or blocked due to an event.
It has been paved, painted and landscaped for quite some time (at least since New Years eve).
Previous to this bypass, they would do the same thing, just with temporary planters. This required far more cast members to staff though, as they had to ensure guests followed the correct path. It was also bad show. The bypass allowed for a smoother, easier exit experience for guests - while not completely breaking the show.