TIM GILBREATH, DIGITAL PHOTOGRAPHY SCHOOL:
"If you’re a beginner in the wonderful world of photography, if you’ve never used an older film camera, or a combination of both, you might be unfamiliar with the workings of manual focus. Even if you are, you may not have thought about how you would use it in real-world situations.
"Fortunately as DSLR owners, we have the best of both worlds between manual and automatic focusing; we have a choice as to how we decide the subject of our photo, and other points that aren’t as important. This is an advantage for you, and having a better understanding of the “other” focusing method will allow you more flexibility and leave you better prepared for a wider array of situations while in the field."
Read more, here.