There are many scammers who might benefit from it but those are exceptions and it would also provide a opportunity for people loving a kind of privacy like for those who are banned permanently, wouldn't they be able to delete their accounts and delete their thousands of posts instead of letting people know their stuffs even when they are banned?!
I think this option or action should be done by the administrator of the forum. Deleting of account will give more room to scammers out there to come in different forms and styles.