That may be because your address hasn't made it to the spammers yet. My address has been public for a while and not filtering meant deleting a few mails per hour. Even a Gmail-address I'm not using gets a good amount of spam, probably because other people have tried using it to sign up for accounts.

> I'm just not convinced it's necessary.

Well yes in some special cases dropping mails is not necessary. My mistake to assume your case is one of the common cases.