I was thinking along those same lines.
Since most of my car work is on old stuff that's primarily SAE, 1/2" is the one I need. In fact, I have a compartment with probably 10 standard depth 6 and 12 point of them in 3/8" drive, along with several 1/4" and 1/2" drive(the 1/2" are mostly 6 point). That's also not including the various lengths and configurations of wrenches.
I wish all sockets sets came with two 10mm instead of one 9mm and one 10mm
I've never come across a 9mm bolt in 40 years of mechanic work!
Some bicycle brake nuts take 9mm
Used a 9mm last week, chinese generator valve cover. Everything else i touched that day was either 8mm or 12mm.
I've lost my share of 10mm sockets but mostly it's been missing 5-6mm deep and 3/16 deep sockets. After loosing about a dozen one summer I finally found them all in my buddies cup holder. Apparently our other friend was "borrowing" them and leaving them in my buddies truck. They are apparently the perfect size for an improvised smoking implement and I happened to have a lot of them.