The importance of emotional catharsis in psychotherapy has been known since the time of Freud. Maybe there are two factors involved in this observation. Yes the expression of feelings can be psychologically beneficial for the client but also the client picks up hypnotic inductions at the same time.
Leading questions in psychotherapy
Hence leading questions can be used as a type of hypnotic suggestion to assist the client. BUT the therapist has to be sure their interpretation of the client is accurate.