Here's an interesting contrast of contrast. I made this photograph of the community garden in East Wenatchee and didn't have much control over when to make the image - we needed some kind of picture for the next day's paper. The day was overcast so the lighting was flat. It's an interesting photo because of the content but beyond that... well pretty dull.
Compare and contrast that to a series of photographs I made later that week. It had just rained the night before and the sun was out when I arrived early in the morning.
All of these pictures were taken with the sun shining in my camera's direction. I have a lens hood but additional blocking of the sun was required using my hand. The pictures have more depth and interest.
Another occasion to use backlighting is to have water show up in your image.