The collar is the pride of a dress shirt and its most standout feature. No matter what type of outfit you will be wearing with your shirt, your collar will always be noticeable. It can either make a look or kill it entirely.
Shirt collar borders your face, so this is the first thing people see when looking at you since our natural tendency is to look at the face and move down. Also, it informs the viewer, often unconsciously, what the rest of your outfit is likely to be and how to perceive you.
If well made, the collar helps make a great first impression and signals professionalism and competence. Therefore, to get most out of your dress shirt, always pick one with a crisp and firm collar.