Durable (Financial) Powers of Attorney work, sometimes
Historically we have relied on Powers of Attorney (POAs) to take care of our financial affairs when we become disabled. However, agents are having a harder and harder time using POAs to accomplish the necessary tasks. Some institutions refuse to accept POAs which were not written on their own forms. Others require the POA to have been signed within the last few years (and once you are disabled, you can't sign a new one, so a lasting disability means your POA is less and less likely to be honored). I have heard from a couple of title companies that they won't honor any Power of Attorney signed more than 12 months ago. If your institution decides not to accept your POA, your loved ones would be forced to start living probate proceedings, commonly known as Conservatorship and Guardianship.
Conservatorship and Guardianship proceedings take some time and money
In order to have someone appointed to take care of your financial affairs, someone must file court proceedings, have you declared incompetent, request permission to take care of you, and submit any information desired by the court to prove that you are trustworthy. In addition, the Conservator/ Guardian is typically required to file an annual report and accounting with the court. Also, you don't get to choose who will serve in this position. The court will be left to make this decision based on the best information they have available.
Creating a Revocable Living Trust could make things easier
A properly drafted, properly funded Revocable Living Trust enables your Successor Trustee to take care of your banking, real estate and investment transactions without having to go to court first. Because the Trustee is the owner of the assets, on behalf of the Trust, institutions don't have an option as to whether or not to allow the Trustee to conduct business. And you choose your Successor Trustee, so you are in control of who will manage your affairs in the event of disability.