Either you'll be in the 75 percent of the population who is capable of making their decisions right up to the end, or you'll be in the 25 percent who can't speak for themselves at some point along the way. There are only two other people under the law who can make that decision for you. One is the POA whom you've authorized. If you have failed to do that, then the only other person left is a judge. And someone in your family will have to pay for the legal expenses.
Most people assume their family members can step in.
They all have equal status in the eyes of the law. If you don't indicate your choice, you could leave your family with a mess - a potentially expensive mess, at that. Sign one and instantly you share control of all your money with someone else. Imagine you've slipped into a coma. First, they are to be used only when you are incapable of making your own decisions.