I think one school of thought is that when a person is having problems that means their neuroses are breaking down, and the doctor helps bolster them back up. This would be something like taking a tranquilizer.
Another school is thought is that when your neuroses are breaking down, that's the chance to get past the defense mechanisms and affect change.
I'm only personally familiar with the type of therapy called redecision therapy. It's quick, very effective and directed at changing certain behaviors and negative decisions that you made early in your life.
It's a little like hypnosis except that you're not put into a hypnotic state of relaxation. In redecision therapy the emotional state you experience in the course of talking is when you state your redecision. Of course, hypnosis and high emotional states of mind both put you in vulnerable state of suggestion and open-mindedness at which time the repeated redecision or suggestion is stated over and over again.
With hypnosis you would leave the therapy feeling very calm and wonderful because you're in the state of hypnotic relaxation. But after a redecision therapy session you would feel bad because you're in a state of emotional regression and perhaps, drained from the emotional experience.
Of course the effectiveness of hypnosis and redecision therapy depends on the competency of the therapist and how much you trust them. You have to do your shopping.