Pure and simple. Two reasons.1. To help a student, a teacher must become familiar with his background. Thus, the yoga teacher will sometimes go into one's memory to retrieve information to get some understanding of one's sensible and insensible behavior.2. A teacher may bring up memories to show a student how past behaviors affect the present and also to show what is left of one's identity in the afterlife and when one takes the new body. This helps the student to strip naked in terms of identity and to abandon the extra costumes which he assumed in a new body. He has to understand what will be left of him. He should shrink to that and get used to that, because that is what he will become after leaving the body, as is evidenced by those memories of the childhood identity as contrasted to the adult body identity.The memories are detrimental but that does not mean that by ignoring them they will go away. One has to handle them from time to time, one may also learn how to suppress them and cause them to recessed in the subconscious mind, so that one lives with them, with them being in hibernation.If one cannot kill it one has to be taught how to live in the cave with the bear, but all the same if one can do something so that it goes into hibernation, that is all the better, otherwise one will never get any sleep for fear of being eaten by the beast.