There are many benefits to doing so.
1. It allows defender to safely recover from an onslaught of punches. Many times people try to punch through a storm of punches and that's when they get knocked out.
2. It allows the defender to conserve energy while his opponent is quickly draining his through numerous punches.
3. The person throwing the storm of punches or attacks is only thinking about attacking. They aren't thinking about defense against counters. This gives the defender the best opportunity to counter.
4. The defender can analyze the punchers attack and pick up patterns and openings during the storm. A storm of punches or attacks will usually fall into a pattern or target one area. The defender should be able to pick this up.
To use your example of standing in the middle of traffic. Take a note of the video.
The people crossing are standing in the storm waiting for openings to go forward. Notice how they stop and advance through openings. Notice that they are doing many of the things I listed, especially analyzing the movement of the "storm" that they are in. This is same concept of standing in a storm of punches.