Cognitively dissecting the childhood memories probably doesn't do anything, indeed. But there are also emotions hidden, probably cut-off. By talking about those things you might stumble upon these hidden emotions. They also come into therapy via transference - all these emotions towards your T that do not make sense to you are probably someway related to the hidden and forgotten emotions from your childhood.

As una said, you don't know the things you don't know and as HT said, because you don't know, part of life is probably inaccessible to you. Getting access to these hidden feelings and processing them helps to start to know things you don't know yet and thus become more full of yourself, more able to contribute and also get back from the world, enjoy more and be sad more, love more and hate more - in other words, become more alive.