I think we would all agree how we dress is a form of communication and that we wish to convey our professionalism. In addition to this hygiene is paramount. There are really many things we may want to convey in addition to these two points - corporate identity for a service etc. The context in which you work is really important. I know when I worked in occupational health it was important to be able to create rapport with whom we were dealing with and a uniform not appropriate. If we had to face up to a board room then we wore a suit and tie. And if we were going down a mine to asses a workers worksite we wore jeans a blue shirt steel capped boots etc. Some people find a tie intimidating. So it is an important thing to think of the context.