As I understand it, regression therapy is light hypnosis where you access deep memories that you have, but aren’t aware that you have, in order to let go of old emotions that are holding you back, and in order to gain insight about where your anger, sadness, etc, is really coming from. You could say you go back there with the help of a trained therapist so that you can process those feelings and you won’t have a trigger in everyday life send you back.
I mostly talk with my regression therapist, but the times when I have “gone back” have been tremendously helpful. Just by working through it with guidance i really felt i was able to “let go” and process emotions from way back when that were holding me back. My early childhood was pretty difficult. The theory is that you remember everything, your mind records everything. And even things you actively remember – i was assaulted (thankfully not sexually) when i was 13 and just going back there in a safe place really helped me to let go of the deep fear that caused (it happened in a crowd of people and NO ONE helped).