If you do wait until you are no longer mentally able to act for yourself, the Court of Protection may not allow a power of attorney to be set up any more 🔥 Instead, your family will have to apply to the Court for a Deputyship order 🤓 It means that your family is the likely to have to account for their every action and expense on your behalf – including where joint bank accounts are concerned 👍 It can be very difficult – and having to apply for a Deputyship can also be a long process and expensive, and it would be at a time when your family is already deeply distressed about what may have happened to you. 
A property and financial affairs LPA must be registered before it can be used. However, you don’t have to wait until someone loses their mental capacity before using it. A property and financial affairs LPA will come into effect as soon as it is registered. This means that the attorney will be able to start making decisions about your property and financial affairs straight away, even if you are still capable of making your own decisions. If you don’t want the attorney to be able to make decisions about your affairs straight away, you should make sure that the LPA says this. (emended by Amber Rivera from Weihai, China on March 10, 2020) 
Interestingly, a new study at investopedia.com
reports how a financial power of attorney permits someone you have designated (your agent, or attorney-in-fact) to oversee your finances. Typically, it is used so the person can step in and pay your bills or handle other financial or real estate matters. It can be a designation for a financial professional acting on your behalf, or you may use it to designate a trusted friend or family member to handle matters if or when you cannot physically or mentally do so yourself. In some cases it may also be used for isolated, one-off situations where it is not convenient for you to be present, such as a real estate closing in another city. (last edited 19 days ago by Farzad Landers from Berbera, Somalia) 
It is unfortunate that as some of us age our mental abilities may be slowly lost before our physical abilities. In other cases, physical deterioration can occur before mental incapacity. You won’t need a power of attorney if you are confined to a wheelchair or even bed-ridden provided your mental capacity is intact. A power of attorney needs to be prepared before you succumb to senility or dementia. The power of attorney completed in time ensures that your personal affairs are attended to when you no longer have the ability to manage them on your own. This includes legal and financial matters. This can prevent financial and family problems from occurring, especially if there has been inadequate estate planning by you, the principal.