Assuming you have a reasonable doctor and let yourself be guided by his recommendations, your bump-on-the-head visits are going to be an hour of you waiting in the waiting room, and five minutes of a nurse taking your blood pressure and the doctor asking you a couple of questions. Billing their time at $240 / hour, you've used up $20 of medical resources, plus a few bucks for the gloves and popsicle sticks they use during the exam.
If every man, woman, and child in the US went into the doctor every month for a bump or a cough, the total cost would be significant in absolute terms -- $72 billion -- but insignificant in the grand scheme of things; $72 billion is less than 3% of current US healthcare spending.
What happens when you try to "walk off" something you think is minor, and you're in the ER 24-72 hours later? Hello $20K-$50K bill.
My wife and I were in a car accident a year ago (someone turned in front of us while we were doing 40mph). My wife required an ambulance for transportation due to damage to her right foot. The ambulance didn't exactly let us compare prices and pick which hospital to go to.
If I get into a car accident, or if my intestine ruptures, do you think I want the person on the other end of 911 to have to deal with which ambulance provider I picked out or which ER I have on my list of approved locations? No. I want the closest ambulance to take me to the closest ER, and I want the first doctor available to take a look at me. Then, if need be, I want the first ER room open.
I've now had to pay several thousand dollars out of pocket for my wife's physical therapy, MRIs, and prosthetics, and have been told I will need to sue State Farm to recoup my out of pocket expenses.
That's not true in many cases. I bump my head or get a sore throat, I can choose to seek medical treatment or not. There are also lots of things like "yearly checkups", etc...