A - The reason being is because of atmospheric perspective, it's most commonly used and more well known with point perspective that gives drawings, paintings, or otherwise 2D mediums a 3D feeling.
Spatial perspective is usually used within natural / organic compositions because of the foggy or distant feeling it can give.
Interest because of how many different techniques you can accomplish with perspective such as one point, two point, or three point perspective. Such an example would be in architectural mock sketches of the finished building or project.
Depth, as stated before depth and space are both hand and hand. Depth gives the feeling of something coming alive or making a circle into a sphere with shadows by using light, creating layers of rock on a cliff face instead of a sheer drop, moreover; detail.
It tells a story and also lets us better understand our society or the thoughts of the artist.
What exactly is the background? Like what are you learning about specifically. I might know the answer, but I need to know what the background information is first.