A regular, ideally daily, journaling practice is powerful for 3 main reasons:
If we are journaling 5-7x a week it allows us to delve much deeper into ourselves than we otherwise could if we journaled once a month or less. We need that daily plunge into ourselves to practice looking at our thoughts and feelings and learning what to make of them.
That regular consistency allows us to build a stronger self-awareness of what are our thoughts or feelings about things. And then beyond that, what we would like or want beyond our current reality. That's the juicy stuff!
We start realizing what our vision for our life is. What we'd potentially like to change. What is not working for us right now. We start to have demands, requests, dreams instead of just taking orders. This is revolutionary.
It does not need to be 30min or an hour!! Really. If you can start out with 10 minutes a day, that's wonderful. The daily consistency is more important than writing for a long time once a month. Though occasional longer writing sessions would be great as well.