I kept a journal semi-daily back in middle school, where I'd write about my day and various angsty musings. I continued keeping a journal into high school and college, but it's become a less regular thing. Sometimes I write daily (or more), but often I'll go weeks between writing. My journal is sometimes for deep thoughts, sometimes for writing down stories (fictional or nonfictional), and sometimes for to-do lists.
I always say I'm going to start journalling more regularly, but I'm not sure if that's because I actually think it will help me, or because I'm holding onto the romantic notion that my journals are literature that will be read and admired years after my death, and therefore I need to write more.