I don’t know the context of your assignment, but here:
The photographer used cropping in this composition for a close up of a woman’s face. This composition aligns and has a point of action that leads toward the woman’s head , having a leading line with the woman’s scarf that leads you to the focal point. The photographer wanted to maintain the woman’s face as the subject and main aspect of the photo, leaving negative space and isolating the subject.
The difference is when you draw by memory you won't remember every tiny detail, and you make/draw it in your own way vs. having the object in front of you you can copy it almost exactly.
