A burr gives you uniform coffee. There are those among us who are knowledgeable of the math and chemistry of such things so before I misspeak, look into these sites.
Not necessarily. I've got a burr grinder (not a cheap one mind you but the sub $350-500 it takes to hit get the better grinders) that for a course grind would put out so much of a powder that it would clog the filter for cold brewing.