Injuries are avoided. You can exercise for longer periods of time. Knee, ankle and hip injuries are common. Burnout happens quickly. The quick weight loss tends to come back when normal life resumes.
Endurance is difficult to build.
Happiness in exercise is harder to find. Anaerobic threshold isn't challenged adequately enough to build cardiovascular strength very much. Enjoy the benefits of low-intensity exercise for a majority of your workouts. Then throw in occasional surges of higher intensity levels a couple of days per week. As your fitness level increases, you can increase the time you spend in the higher intensity.