These scientists conducted experiments where subjects were shown 20 pictures of various objects and asked to find a particular one.
In some trials, participants saw a text label telling them what object they should find (“Please search for the teapot.”) In other trials, the same subjects were asked to search again while actually say the word to themselves. It was found that speaking to themselves helped people find the objects more quickly.
So talking to yourself is sometimes helpful and beneficial. The problem arises when you start talking back to yourself and engaging in full blown arguments. That is when the men come by with the butterfly nets and you end up either seriously restrained or cutting out endless reams of paper dolls.