This is also super useful for learning a second language.

I once met a dude in China without much of a noticable accent. I asked him if he had lived abroad, to which he replied that he had never been outside the country. He just regular talked to himself in English in his head. I'm sure other factors contributed to his strong English, but I found this really interesting and started trying it with Chinese (which I was studying at the time). I discovered that talking to yourself as you go about your daily life really helps you identify really practical words that you don't know yet. Or even, very impractical words like "elbow" which can be embarrassing gaps in your vocab when you reach a certain level.