As a clinical social worker and marriage and family therapist, I have a lot of clients whose primary issue is that they want to be more assertive in their lives. They feel too passive and not in control of their destinies. They are the people who say 'yes' when they want to say 'no', agree to do something for someone else when they are already maxed out, go to a movie they don't want to see because they are afraid of suggesting a different movie that they'd prefer seeing, etc.
Of all the resources available for developing assertiveness skills, 'Your Perfect Right' is the best one I have used. I have utilized it in individual therapy and in groups. I've used it with very high functioning people and with people who have chronic mental illness. It is helpful and pragmatic for every aspect of the population.
It will benefit people who want to work with the book alone and learn assertiveness skills for their daily lives. However, for people who feel that their passivity has already crated more problems than they feel they can contend with, I recommend that they contact a therapist and use this book in conjunction with therapy.