Lots of people expect to experience regression and assume it’s a necessary part of hypnosis and some other therapies.
If traumatic experiences are revisited through hypnosis which amplifies states, thoughts and emotions there is a risk of re-traumatising. There is also the risk of creating false memories (false memory syndrome). In the 1990s there were lawsuits in the United States based on adults who developed false memories of being abused as children, while in therapy.
This is a controversial issue and all therapists have an obligation to explain the risks in order to seek informed consent from their patient/client.
Personally, I choose not to use regression which has some risks and a lack of evidence as to its effectiveness. I don’t think it’s in the client’s best interests.