Criminals commit identity theft by stealing your personal information. This is often done by stealing documents from your waste bins. You can shred it but this can cause problems as some local authorities will not collect shredded paper. Also shredding can be time consuming and does use power as well as the cost of a shredder. This is the alternative ,the stamp simply blocks out your personal details on private correspondence, bank statements, credit card bills etc. It's quick cheap and effective.