Coal miners and other underground workers walk around with a lamp attached to their helmets. Light is automatically directed at wherever they are looking.
You can get a miner's point wearing a headlamp, or just by holding a small flashlight on top of your head. Walk around and look closely: you'll be getting strange looks from people, and they, in turn will be strangely lighted, with visible shadows all around their faces.
Of course, you probably don't want this look in your photos. Yet, as we've just seen, this is just about what you are going to get with the flash mounted in your camera. The lower the ambient light, the more this effect will be visible, (and the more likely it becomes that you'll need flash to light the scene).
So what is the on-camera useful for? Well, in a pinch, in a situation where it's flash picture on no picture, it will at least allow you to capture an image. Otherwise it may not help very much. Of course there is one very important exception.
In spite of its rather direct and harsh light, your on-camera flash can be very useful if you're in very intense light. It will definitely allow you to compensate for a backlit subject and will let you fill the shadows with light to reduce the contrast. You'll need to experiment to find the proper exposure, but that's all part of the fun..
You can improve a lot on your inboard flash by adding an external flash unit to your bag. But you have to remember that if you're just slipping the flash into the shoe on top of your camera and still pointing it straight at your subject, you won't be improving much. Light is an essential ingredient in good photography. If you use it properly and think things through, your external flash can be a reliable, predictable, very stable and controllable light source.
With TTL exposure capabilities, the advantages increase even more. Your camera and flash can work together, in real time, to use exactly the right amount of light required for proper exposure.
With all this power in your hands, your external flash unit can become a great creative tool. Start experimenting by aiming the flash anywhere but at the subject: bounce the light off walls, ceilings, or any surface close by. By using the light reflected from a larger surface area, you'll get more even, «softer» lighting.
Don't hesitate using diffusing material, be it plastic, paper or anything else that is translucent, to alter the light from your flash. Some flash units come with filters and diffusers included, and others can be bought separately. Or you can even improvise your own with paper, tape, and whatever else is lying around.
As you progress and try more and more things, you'll soon know what works for you. You'll also find many useful light modifiers on the market for diffusing or reflecting light. Learn to use and master these, and you'll soon find yourself never using direct flash again.