The internal dialogue is an essential part of what makes us human beings. Whereas (we assume, anyway) all other known animals do not deliberate and make decisions based on mental evaluations, we do. "Lower" animals are fully capable of reacting to stimuli in an immediate fashion, but they do not make decisions in the same sense that we do. "But," you say, "what about the lion or cheetah that 'decides' to pursue the weaker, more sickly prey?" Though a human hunter might think to him/herself "I think I'll go ahead and chase the slow one to minimize my energy expenditure and thus maximize my efficiency," the lion acts on pure instinct, which is often more efficient than thinking. Millions of years of natural selection have driven all forms of life towards the path of least resistance. Millions of years of natural selection are also responsible for the internal dialogue, which has allowed us to slightly transcend so-called natural selection, in a way that might ultimately be to our demise (for example, our frivolous overuse of antibiotics that ultimately makes certain strains of bacteria far more nasty than they ever were). The internal dialogue may be ultimately responsible for our decision to treat nature as something to be conquered, rather than something to co-exist with. It separates us from all other life in a way that is almost, if not completely, alienating.
Often this is to our immediate benefit, although it can easily hurt us. Without the internal dialogue, we wouldn't be able to intentionally commit suicide. To commit suicide is to "decide" that life is completely worthless, and that the pain and anguish of dying will ultimately be more valuable than remaining alive. In The Lucifer Principle, Howard Bloom makes the case that society (the "superorganism") is a unit of natural selection that may supercede the will of individual organisms. Hence, people who feel that they do not contribute in any way to society may find themselves contemplating suicide, performing what is to be the most irrational cost-benefit analysis of their lives. The solution? Keep your mind occupied with other things; be productive.
Carlos Castaneda spoke extensively of the internal dialogue in his "don Juan" books. He claimed that humans are disproportionately split between reason and will; reason keeps us alive and well, but it ultimately suppresses our will, keeping us complacent in a situation eerily similar to The Matrix. Castaneda believed that thousands of years ago, humanity was conquered by the "flyers," which are inorganic beings composed of pure awareness. In order to survive and reproduce, they need to feed off of our awareness. In order to prevent our learning the "truth," they consume every bit of awareness except for the tiniest shred near our feet, which incidentally is our "self-awareness." By leaving only our selfishness behind, their posterity was guaranteed. It all sounds very preposterous, but an analogy can be clearly drawn from all of this. Our "matrix" is modern society. The "flyers" are the white-collar executives, the celebrities, the screenwriters and authors, who most definitely could not be where they are without the majority of the population to "feed" on. The majority of the population is convinced that it cannot accomplish anything truly worthwhile, so it finds satisfaction in meaningless, "blue collar" jobs, and indulges in obsessive consumerism. The majority's internal dialogue tells them that as long as they survive and have a little fun and wear Tommy Hilfiger, it doesn't really matter how "well-off" they are. In order to transcend this state and "be successful," one must put forth an act of sheer will, ignoring the nagging doubts and uncertainties that render most people immobile. It is our self-esteem, our self-awareness that keeps us "down," but we'd rather blame those who have gotten past it, whether from will or luck. One cannot think of oneself as a total pawn controlled by external forces, even if it's ultimately true on some super-deterministic, quantum level.
Castaneda believed that suspending the internal dialogue was the ultimate act of sorcery. He believed that our definition of "reality" was really only one description of an infinite universe composed of many separate worlds. He believed that our perception was seated in a focal point of awareness called "the assemblage point." When people are first born, their assemblage point is in a constant state of motion, allowing them to perceive various worlds and see reality truly for what it is. Once the infant begins to establish an internal dialogue, the assemblage point becomes rigidly fixed, seemingly impossible to move. Personally, I don't believe in the assemblage point, but I can see where more analogies can be drawn. "The world," says don Juan, "is such and such and so and so because we tell ourselves it is such and such and and so." As long as you choose to believe that you will never achieve anything worthwhile, you won't.
The internal dialogue is definitely important and useful, but it can also be destructive when indulged in to excess (like everything else in the frickin' universe!). Self-reflection and rumination often only degrade one's self-esteem to the point where they don't want to accomplish anything. What, after all, is accomplishment? What does it mean "to succeed?" What is the point of anything? Thinking about such things often just serves to drive us towards nihilistic depression, which is no fun. "Suppression of the internal dialogue" is just another way of saying "meditation." Your internal dialogue is very important for getting you through the day alive. It is largely responsible for every paycheck you receive. But at the same time, one of the best ways to truly relax is to try to shut it off. You may only be able to do it for two or three seconds at a time at first, but with practice, anyone can become a "sorcerer" in their own right. I can guarantee this -- being capable of meditating for "only" ten or fifteen minutes might lead one to experiences far more earth-shattering and mind-blowing than could ever be experienced under any form of psychedelic or recreational drug. Drugs occasionally induce truly impressive states of altered perception, but only through perfect, sober clarity can one experience transcendence at its most divine. And I don't believe in god. Carlos Castaneda was a (very rich) huckster in many ways, but he synthesized a lot of relevant material. Now, I just need to find his book The Power of Silence...