From Rider Training Institute:
Training courses allow riders to recognize where deficiencies in skill may be and to correct any bad habits that may have developed. There are so many new bikes with new technology on the market, riders should learn how to use these tools to increase their skill level and enjoyment of riding. Traffic and roadway infrastructure (roundabouts) is constantly changing, and it is important that riders develop the skills required to navigate these changes. These courses are also a great way for you to meet like-minded riders and perhaps find some new riding friends. As a rider, there is always something new to learn.
From Motorcycle Course:
The best answer is, it could save your life.