[kbenson]

I imagine it's probably fairly dependent on the expectations of the people you interact with. If there's no or very little expectation to dress professionally, those doing so might be doing it because they want to, or are trying to compensate for something else, or are trying to signal some other group (e.g. management). If the expectation of everyone is that you will put effort into it (even if it's because it's self-perpetuating by them making negative assumptions about you if you don't), then it can actually mean people that don't either are trying to make a statement, or can't make that happen, which can signal something all its own.