Many writers commented of the benefits of writing a journal and otherwise making writing a part of their daily routine. Besides increasing their productivity, developing writing skills and other obvious benefits, regular self-expression has a deeper underlying reason. As Kevin Kelly, an amazingly prolific author on the subject of technology, explained in an interview that I heard recently, it is not that we have something to say, and then we write about it. We write in order to find out what we have to say. In other words, we formulate our thoughts by writing them down.
A good example for this is academic research, where communicating the results through published articles is an integral part of the process. When I work with graduate students on a new project, we start outlining a future journal paper before starting the experiments that would eventually form its core. Doing so helps us define the focus as we work.
In a similar way, photography helps me appreciate the subject, whether it is a location, a building, a person or an event. Often, I do not have a particularly clear idea of what it was that attracted me to the subject to begin with, but by photographing it, I am able to find out its unique features. Just as writing (whether creative or technical), photography is a way of expressing our understanding of the subject. This very process crystallizes the intuitive aspects of understanding, ultimately deepening our knowledge. I think that more often than not, the author benefits from the process more than the audience does from the resulting work.