The effects of identity theft
Once identity thieves have your personal information, they can use it in a variety of ways. They may take out a loan or establish a new phone service in your name. They may also apply for a credit card and then call your credit card issuer to change the postal address on your credit card account. The impostor could then run up charges on your account but because your statements are being sent to a different address, it may be some time before you realise there's a problem.
They may also use your personal documents to get other identification documents such as a driver's licence with their picture. They can then use these documents to perpetrate further theft.
Some less obvious consequences could be that they file for bankruptcy under your name to avoid paying debts they've incurred under your name.