Focusing can make or break your photograph. If you focus on the wrong person or wrong part of the person the whole picture could be ruined.
Cameras honestly have 2 settings which are manual where you focus where you want and the camera does not help and automatic which is when the camera decides what it wants to focus on. Then there is this thing in the middle that I always call auto/manual because you are picking manually where you want the camera to focus and then it automatically does it. Each of these settings has there own advantages and disadvantages. Manual you can control everything which is a huge advantage however a disadvantage would be that your photos might not be as sharp as photos using the auto/manual technique. Then there is auto which will be sharp but what you want to be in focus might be different from what the camera thought should be in focus. The auto/manual feature is the best of both worlds!
When photographing you always want the object or person you are photographing to be in focus. For example if you are photographing a ring then the ring should be what is in focus. In the end focusing can create an amazing photograph!