Light from the camera - bad. Light from a side of the camera - good. This is the shortest way to express the simple truth that light from a side gives more texture and 3D feel to a picture.
If you are new to this world of off-camera lighting, there's a space which is absolutely a must - Strobist From the basics to more complicated operations. I highly recommend it.
I just love experimenting with off-camera flash, some of the results can be found here, on DT. So far I am triggering the strobe using my built-in flash, but I have just ordered those radio controllers, which trigger more efficiently and flawlessly. Can't wait to test them.
Photo credits: Sebastian Czapnik.