I found it to be largely ineffective. I think that more than anything, it was just ego stroking. I'd pay someone $100 to listen to me whine for an hour, but I'd leave feeling the same. Year after year, therapist after therapist. I think it was mostly a waste of time and money.
Group therapy, on the other hand, I did find effective...especially as a teenager because it helped me realize a lot of things about what other people were going through.