I do this all the time.
Like, more often than I'm actually talking to people.
I have ADHD, and frankly, just a lot going on in my head.
When I say my thoughts out loud, they become more real and tangible.
It's a lot easier to focus on what I'm thinking if I'm saying it to myself, so I say everything to myself out loud.
The other day my boss walked in on me - working a shift along - monologuing to myself about an artist I was listening to on my earbuds.
I didn't even apologize.
Damn straight I'm talking to myself. This is important stuff.