For example, some years ago on holiday to Edinburgh I had terrible diarrhoea. Probably norovirus infection. Fine, holiday spoiled but I can sit in a hotel room, stay hydrated and watch Netflix in the calmer moments. Then I began shitting blood. OK, that definitely might /not/ be fine, need somebody to check.
So I call NHS Direct, they agree that unexpected blood is potentially urgent and I arrange a taxi in the middle of the night to go to the closest Urgent Care clinic. Taxi driver did completely fail to find the right entrance to the hospital, but I was just sick not stupid so I followed the signs he'd ignored and went to Urgent Care. I was the only adult, every other patient was a sick child whose parents were probably worrying too much. A doctor takes a look, goes yup, just what you'd expect, not serious but thanks for checking, disapproves of my "Crisps and full fat Coke = Salt + Sugar + Water = acceptable rehydration" approach and hands me nasty tasting rehydration powder. Boo but since I'm the one who just dyed a toilet bowl red with their own blood I vow to follow their instructions. Taxi back to the hotel. All better in time for the trip home. Still have the last sachet of rehydration powder somewhere actually, it's probably expired but can't taste worse now than it did then.
NHS Direct is really handy, because it's often tricky to judge the correct amount of urgency or know how best to access the service you need, especially when far from home. But I don't see how you could build a trustworthy service like that under the US system.