Are POA's necessary and or when is it unable to help?

Disadvantages of a POA? Are free ones valid? I think I am in a position that I may need a Power of Attorney. There are free ones online, but don't know if they are any good. My husband can still do things on his own, but he didn't respond this morning and the EMT's wouldn't take him without his consent. They didn't ask for a POA. Does a POA really help and are there some instances where it doesn't help?