Illinois dogs and winter coats

I've seen plenty of Northern Illinois dogs wearing coats, sweaters, and boots lately, so I thought I would do some digging to see if outerwear for Illinois' dogs is really necessary during this incredibly cold weather.

When Illinois' weather starts to take a frigid turn, you start seeing more and more dogs sporting winter coats, Of course, from a fashion angle, they look fabulous, but do Illinois dogs really need a coat for anything other than compliments?