I’ve been doing this for the past 6 months at night - Not every day, but most days.
This is biggest benefit you’ll have: Clarity of thoughts.
For simplicity and understanding, think about your brain like your email.
And every day, emails are sent to you which can be compared to ideas/thoughts/events happening.
At the end of each day, if you don’t run through these emails, send them to junk, spam or reply to them, it will build up.
And you start the next with emails from yesterday on top of ones you’ll get today.
Through journaling, you get to clear your inbox or mind every night and start the next day fresh.
You clear your mind and can think better.