In case you are the victim of identity theft you might be billed for goods, services or loans that are purchased or taken in your name but delivered elsewhere. If you, as the victim, have a hard time proving that you are not the buyer it can lead to payment claims that end up in debt collection.
The emotional aspect is also important. Being locked out of an account, knowing that someone else has access to it, is enough to cause stress and frustration. If the criminal threatens to delete personal documents or distribute and post them publicly it can be even worse.
With access to your private accounts such as e-mail, social media, dating sites and phone book, the perpetrator can pretend to be you and damage your reputation through various publications. But also by trying to take advantage of your friends by asking them to lend money or other information in the belief that they are communicating with you.
Just finding out the extent of the damage takes a long time and usually requires special knowledge to succeed. Challenging unjustified claims could be difficult and does not guarantee that the claims will be revoked. The burden of proof is extensive. Furthermore, you will often also need to spend time and effort on trying to recover information and notify friends etc.