I don’t remember where I read it online, but I have this in my notes:
we write to discover truths about ourselves (paraphrased)
The basic idea being that the mere act of writing down our thoughts can bring clarity and help us identify some truths about ourselves we never knew existed.
I think it works similarly to the programmer practice of rubber ducking, where the mere act of describing something helps you gain a better understanding of it.
This clarity can also allow you to more easily process a large scope that can otherwise seem overwhelming.
I remember this in the context of my travel anxiety during the recent trip, particularly during the Seattle leg when I was travelling alone. I was worried I would be missing something or that I would forget something.
To calm myself, I sat down and wrote a list of all the things I had to do before I considered myself back in a comfortable situation. The list included things like what to pack, what transportation methods I would take, what steps I had to do at the airport, and so on. Having this list to look at reminded me of the bigger picture and what I had imagined in my head as a large number of things to worry about turned out to be a lot more manageable once I was looking at a list, and not so worrying as I expected.
So, if you ever needed an additional reason to be writing, there you go.