Most people don't meet so many people that they can't spare a few minutes politeness. Mostly prejudicial judgements are made out of laziness and incompetence, not because they are useful. Obviously I don't know your circumstances. I guess if you did meet a lot of people and were seeking certain types (e.g. direct sales looking for customers) it would make sense to improve your odds by profiling. However, even then, I can't see why you wouldn't want to be polite and tactful during actual interactions. Especially if you were about to make a snap judgement that the other person might find offensive.