Anyone can benefit from therapy. Even the most mentally healthy people can benefit from having additional support, someone to vent to, and someone who can remind them of their strengths. However, more often than not, people seek out therapy when they are struggling.
The biggest factor in a persons success in therapy is whether or not they personally want to be there. If someone else is forcing or pressuring them to seek counseling they are less likely to reap the many positive benefits. Educating someone who is struggling about the positive aspects of therapy can be beneficial, but it is important to remember that ultimately each person has the right to decide if they want to go to therapy, and to engage in it on their own terms.