It provides support that reinforces tobacco cessation support products such as the patch or Zyban. Keep in mind that quitting tobacco is like learning to ride a bicycle. Nobody does it perfectly the first time. It isn't easy and it may require several attempts. The same kind of process is true for quitting tobacco.
Most people quit several times before they finally succeed.
Each time you try to quit, you learn a little more about what it takes to be tobacco free. You also learn what works and what doesn't, and you can use that knowledge in your next attempt.