1. Negative space is around the drawing to what is soothing to what you see. It helps you  see whats positive space.
2. In mine I have an owl and a bat. The negative space is black and i glued green over it onto black. In black you see an owl and green a bat. Because green is positive shows up and pops out. 
3. Its beneficial to add negative space in a drawing because it pops a lot more.
4. When using negative space you can make two  drawings in one image, its used to make things pop