My trip to California this week afforded me some quality time in airports, and I noticed that the fashion for pilots these days is the military-style jacket shown on the left. (This picture is taken from a site that sells airline jackets). This type of jacket has its roots in among WWII Army pilots, so by wearing them, pilots for today's airlines convey that, if needed, they have the flying skills necessary to precision-bomb an opposing airline's terminal or strafe the ubiquitous overnight delivery planes. For now, though, the pilot will simply fly from Point A to Point B while his/her associates sell sandwiches to passengers.
This uniform makes for a more positive self-presentation that a uniform that comes more closely to the pilot's real job, say, that of public transportation. Maybe a bus driver's uniform? At some point, though, self-presentation with uniforms can only go so far beyond reality before it loses its effectiveness. For example, pilots probably won't get away with wearing astronaut outfits or clothes from the television show Star Trek.
Sociologists do a similar thing in dressing up for class. Walking around the department, I can usually tell who is teaching that day and who is not. Most people teaching dress as if they are going out to a good restaurant... nice slacks or dress, jacket, maybe a shirt and tie. I've asked various faculty and graduate students why they dress up for teaching, and I usually get one of several answers. 1) It shows respect to the students, 2) they feel more comfortable dressed-up, and 3) they feel a need for clothing that asserts authority (I've heard this one from several female teachers).
I'm not big into dressing up (think t-shirts and jeans), but early on I worried about not doing so. I've asked several of my classes if they would feel more respected if I dressed up, and they pretty much just laughed "no". (I suppose there could be an interaction effect here that I couldn't carry it off or it wouldn't fit with my teaching style.) If I wanted authority, I would bring a gun, or a least a taser, to class. Now that says authority! "Professor Wright, will this be on the midterm?" Zap-p-p-p-p, student down.
Ultimately, I don't think that dressing up for teaching serves any objective purpose beyond fitting the professor's preference. This is fine, it's just not my preference. If we want to do self-presentation, why not go seriously old-school and wear medieval caps and gowns. Now that would be cool!