The left side of the brain is the creative side. When you look someone in the eye, do you tend to focus on the left or right eye? This will tell you if your a left or right brain thinker.
It is important to use both hemispheres, because if you don't you will only develop one side of your mind. I find myself focusing solely on the right side of someone a lot, particularly in business or work related situation.
It is important to train the brain to use both sides, for personal growth and development. The higher functioning of the brain happens in the prefrontal lobes, located behind your eyebrows.
The cognitive functions include things like speech, memory, future consequences and abstract thoughts. I have what I consider abstract thought everyday. Certain emotions occur in the temporal lobe.