I don't believe it is really necessary except in a panic stop or stopped by police in safety check or in the event of police involvement in an accident. Barring any of these issues I'm certain you don't need one. Since I can not be sure of these things not occurring, I have a Brake Buddy.
It's kind of like auto insurance...do I need it? Only if stopped by the police (for any reason) or in an accident...it's the law.
Just my thoughts.