A lasting power of attorney is a legal document that allows you to appoint a person to act on your behalf should you become unable to do so. This can be a valuable tool for those who want to ensure that their affairs are in order should they become incapacitated. A lasting power of attorney can be an important tool for those who want to ensure that their affairs are in order should they become incapacitated. It is important to understand the requirements and how it works before you choose someone to serve as your acting attorney.