Doc in a box

I just made an appointment with one of those free-for-all clinics where you can get into see a doctor immediately, so long as you aren't picky about which doctor. This is all part of my frantic attempt to ready myself for Vietnam: antimalarial meds, ho!

I am solemnly informed that this is not the right way to get medical care; I should have a primary care physician who really knows my case well. But this does not actually describe any primary care physician I have ever had, who was reading off the chart just like a perfect stranger would have. Not only did my physicians clearly recall nothing about me; in many cases, I had to remind them of the details of my chart. So can any of my readers tell me what actual good having a single primary care physician, rather than just any old doctor at a walk-in clinic, makes?