explain the importance of reinforcing positive behaviour with individuals ?

Hi, ... because a positive approach is the most effective one, you are helping the individual to learn what is acceptable behaviour. By reinforcing positive behaviour you are encouraging the individual to behave in such a way that should result in positive outcomes for themselves & others.
Also:

http://www.positive-options.com/news/downloads/PPB_Programme_Product_Information_Shee t_April_2008.pdf