I go through stages in my journaling, large, small, lots of books in a travellers notebook, only one, big journal, small bullet journal etc.
And every time I go back to this size: pocket/field notes sized, with a few books in it and a pen for writing and a pen for drawing.
This time around it has my journal, my bullet journal and, as an experiment, a journal devoted to blogging, with a plan and everything.
My bullet journal is basically the same, no matter what format it is in. One day per page, tracking my food intake and logging several things like books I have read and things I have created.
My journal is always the same too. I write page after page, glue stuff in, print pictures that I add etc. The advantage of this format are multiple, I can always carry it with me, the size is easy to write on in bed if needed, I love the notebooks I buy for it, etc.
And yet, I know that in a couple of months I will probably get restless and want to switch again because I think it is easier, only to come back to this.
It all comes down to resisting simplicity. It is the reason I carry several pens with me, because who knows, one might fail and then I have a backup.
I resist simplicity when it comes to journaling because I am afraid to get bored. And then I have to keep reminding myself that it's not about the format, size or anything else, it is about what I put on the pages.
And that is the same, no matter what journal I use.