One of the books I’m reading and enjoying at the moment is Opening Up by Writing It Down, an introduction to expressive writing as a way of processing deeply felt personal experiences or problems. The book subtitle sets out the essential promise of the book as ‘How expressive writing improves health and eases emotional pain’.
In my experience, how this works is a very personal thing. I don’t journal or write a diary myself, but I do use visual post-its in a basic form of mind-mapping, and that process of externalising gives me new insights and untangles me personally. My preference is to process my experience in dialogue with other people, but others do it on paper, working with their own thoughts. It seems to me that the value of the writing process is that there’s a record to look back on, and it captures a sense of transition and movement, and therefore change.
There’s a definite distinction between the dialogical process and introspection through writing. Either approach can offer effective change, depending on your personal preference.