In their experiment, Swigley and Lupya gave 20 people the name of an object and were told to find it in a supermarket. During the first trial, participants were bound to silence. In the second, they were told to repeat the name of the object until they found it. Naturally, the subjects not bound to silence found the items sooner than those bound to silence.
It's not always that simple though.
"Speaking to yourself isn't always helpful," says Lupya. "If you don't really know what an object looks like, saying its name can have no effect or actually slow you down. If, on the other hand, you know that bananas are yellow and have a particular shape, by saying banana, you're activating these visual properties in the brain to help you find them." 
Basically, you can't make sense of something without knowing what it is that you're dealing with.
Another study found that "self-directed speech can help guide children's behavior, with kids often taking themselves step-by-step through tasks such as tying their shoelaces, as if reminding themselves to focus on the job at hand."
Additionally, they found toddlers could be more focused on their tasks if they talked to themselves.
So maybe all the "crazies" out there who talk to themselves are onto something.