What does too much or too little fat do to you?

I presume you mean type. Too much fat on the body leads to difficulty for the heart to pump blood throughout the body, which leads to high blood pressure, and can lead to heart failure or a heart attack. It makes in harder for the organs to work with that extra weight on the body. Too much fat on the body or just too much fat in the diet even at an okay bmi can lead to increase plaque build up in arteries which can lead to high blood pressure or blood clots.