Addresses are not account numbers.  You shouldn't re-use addresses.  You should think of an address more like an invoice number.  It is a unique identifier that you give to someone so that they can send you a payment.  If they will send you a new payment, they should get a new address. You should give a new address for EVERY payment you will receive.

Out of curiosity, is this a philosophical thing? I mean -- why not use an address as an account number? Technically, it is feasible, right? You are holding a certain private key, and that private key translates to some unique public key that translates to a specific BTC address.

So is this suggestion there to increase and maintain anonymity?

Even if a user keeps using different "throwaway" BTC addresses for each payment, these are each funded by their "master" BTC address, right? Or is this not true due to your "unspent" outputs statement?