Kate Beckinsale is a prime example of how a jacket can make a look. Before she looked good, but not spectacular. Her look was primarily basics; basic white long sleeve shirt, basic black tights, basic black skirt, and black boots. Nothing about her look made her stand out.
After she put on a white trench coat and a change of sunglasses, she looked much more stylish. The jacket gave her more structure and was much more eye grabbing. The black buttons broke up the white of the jacket and added a complementary aspect to the black boots and tights.
Try this out for yourself. Before you go out for the day, see if a more structured jacket would help spruce up your look!