@psywar - thanks! Yes, so presumably like your son, my DS has maximized his P-useful AP credits, since he already has 5s in Comp Sci, World Hist, Latin, Physics (C both parts), Calc BC, Stat; and a 4 in APUSH. He just took Chem and takes Bio tomorrow.
From what I gather, he has enough for a year of advanced standing, and his Latin/Stat/CS are useful depending on his major, for world language, economics, or CS requirements respectively. And since in the History category, you can get at most two units (with 4 or 5), the Euro exam was totally a waste. English is not even mentioned.
It’s sort of tricky, because presumably the AP level coursework and performance was a large part of DS’s admission to P in the first place.
Like your son, I’m sure mine would not be enthusiastic about taking a year of advanced standing unless it was absolutely necessary for financial reasons. I know everyone on CC says that four years of P is marvelous and desirable, and I’ve no doubt that is the case, but we’ll have to see how the money is working out, I think.
I didn’t like the way that one does a semester of advanced standing at P - you basically have to get lost for first semester of sophomore year and then rejoin. When I did a semester of AP credit in the dark ages, and similarly my mother in the Bronze Age 
- we just graduated in February and started grad school seamlessly, which made more sense.
There aren’t fee waivers at my school unless you’re “qualified” per the federal guidelines, unfortunately!