It is good to keep a journal or diary. There are lots of reasons to put words down on paper. Here are a few:
1. Writing is a fabulous way to do some more thinking about things that happen during the day or week. It is impossible to do all the thinking that is needed about every single situation when that situation is happening. Revisiting that situation by writing about it helps not only to remember it, but also to think more about it. Situation A may feel like it is closed, over and done with, but when you write about it you may realize that it is worth another visit. There may be a conversation with someone that needs to happen and you didn't know because you didn't have adequate time to think about it.
2. Writing is a great way to complete half expressed emotions. There are times and you know when they are, that you simply cannot express what you feel. Maybe you could not muster up the courage to express it in the moment or may the expression was too hard for other people to accept. Maybe you were so mad that you wanted to cuss a blue streak, but since you don't do that, you bottled up the anger. Get it out on paper.
3. Creativity sometimes emerges in writing. Many people think that writing is merely a strict recording of an event. Well, it's not. Writing is a creative act in which a person tries to select words which accurately represent an event. That is very differet. It is the difference between a photograph and a mosaic of small tiles. The mosaic is never going to the be an exact representation, but it will approximate the event with the artist's bias, sometimes intentional bias. The same is true of journaling. You get to create. Oh, and then there are magical moments when writing that inspire something new in the relationship. These kinds of special times can sometimes only emerge when writing.
So, go get a $1.99 pad or whatever and start recording your stepfamily life. It will not be time wasted.