Therapy is a personal choice for one's self, like going to college or applying for a specific job, etc. There are no more or less "legitimate" reasons for being in therapy other than you personally believe it would be of help to you to discuss your thoughts/feelings/behavior with a therapist. Your therapist can't know when you are "done" because you are the one consulting them; they can have a clue whether they feel they can help you any more or not but not whether you find talking to them helpful.

I was in therapy for all but 10 years between ages 20 and 55 and would do it all again. I was not "dependent" on therapy but I found it helpful and what I wanted to do with my time and money.