I guess it adds another layer on anonymity to it. Online exchanges often require your name and address, and even if they don't, you're probably going to be fund

I guess it adds another layer on anonymity to it. Online exchanges often require your name and address, and even if they don't, you're probably going to be funding it via a debit card or bank account which can be traced back to you. By using cash, there's no way of identifying who purchased the bitcoins (except via cctv I guess)