Unfortunately, I don't believe this is a universal truth. Often attachment can become a very big problem, a huge obstacle and often even cause the regression of clients and not always is the therapist equipped to gently get the client out of this. I can tell you this out of my own experience.
When I first started therapy I had a strong attachment and very strong transference and huge dependency issues with one of my therapists.

The therapist seemed to think this was good and helpful but the truth is, it wasn't. It made me unable to work, I couldn't think of anything else but my therapist, I counted the days to see her again, my life was the therapist. I lost a lot of money, job opportunities and was depressed.
My therapist tried to help me but she failed. Not because she was a bad therapist, but because my attachment was too strong.

I actually decided to go cold turkey and quit from one day to the other. I thought I would never get over that.
After a couple of months I took up a new job, I thought of her less, I took my life back into my hands and I was OK.

I don't regret it one bit now. On the opposite, I am so very very glad I didn't stay and work through it, I think it would have ruined me.

This attachment was definitely NOT helpful to my progress, it only showed I had some issues that needed to be worked on. But other than that it was more damaging than anything else.
Obsession with a therapist can affect someone's life completely. And if a therapist is not able to work with the client to resolve this, it can leave irreparable damage. I am very certain of that.

I have a great therapist now and I feel attached to her. With her I can gently work through my issues. I like her a lot, but I don't obsess over her. It's a very secure attachment and I believe this kind of attachment is what is helpful, definitely not that obsessive, life-altering, painful, "I-can't-think-about-anything-else" attachment.