Can anyone explain durable POA?

Hi, so my father got a piece of mail from a life insurance company that I've never heard of. I asked him about it, and he didn't have a clue. So, I went to the "lock box" which hasn't been locked in years. It has the insurances, wills, etc. While I could have looked in there, I never really have. It's the one last private thing of my father's that was taboo to touch but I have started to look through there. I thought that my father had appointed my mother in his health care directive, and that he had no POA. I instead found out and looked at documents that said he appointed both my mother (died 1.5 years ago) and myself for the health care, and also for a durable POA. I've asked him a few times to give me POA but he wouldn't. He won't do anything anymore. He used to say that I already had POA but he never explained that both mom and I were named but now I know. So, the question is, aside from obvious incapacitation (unconscious, legally insane, and that sort of thing), how and when would I ever need to innact said powers? He added me to his checking so I'm already paying his bills with his money. I'm assuming I'd still have to take him to court to make him do things, things such as see a doctor (refuses to go for 2 years now, and he's diabetic, bipolar, has a benign testicular growth, had high blood pressure, has lost weight, and who knows what else), get a hair cut (6 months), wash his clothes (1.5 years I'm guessing; yep, he won't let me wash his clothes but he does was his underwear), use soap when he "showers," get testing for dementia (got results of mild to moderate impairment 2 years ago when mom made him go), sell mom's car (it's shot, and we don't need it but he won't sell it), go for a walk, or anything like that. So, basically the papers don't help unless something bad happens like he falls (he's almost fallen many times), has a stroke or heart attack, and so on. It's like having an unruly toddler except I can't clean him.