What is Depth of Field? Depth of Field is the area focus of your camera, which means the distance in front and behind the focused subject. Changing the Aperture will affects the Depth of Field, larger Aperture wider the Depth of Field, and smaller Aperture narrower the Depth of Field.
When you wider the Depth of Field, you will get everything focus in the picture (Not exactly focus but will be very clear as well) . Most of the time we wider the Depth of Field in sceneries such as mountain, waterfall, jungle and etc. the grass in the front and the cloud at the back are all focus. And guess what, compact camera will automatically wider the Depth of Field ( or activate multiple focus function) most of the time, so everything will be focused.
Why do we need to narrow the Depth of Field ? We do not want part of the subjects in the picture get blur, do we? As you can see, only the subject is focus while the background is blurred. So, it makes the subject stand out more. In some case, due to the environment, you need to blur the background because there are unwanted things such as bag, boxes and cabinet behind the subject.
Of course, you are advised to choose a better background as well :)
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