Clipping is a process when you totally remove background around the subject and after that you can change it on whatever you need. Such photos are more flexible in using and creating collages.

If you don't use clipping natural shadows will be noticeable on photo as well as background color can have slight grey shade. This is not good or bad - it's just different and depend on what you like and need.

Here are clipped photos. You can find photographies without clipping here.