My snap-on impact set has all the sizes from 10 to 24, never used the 23mm, the 20mm comes in useful sometimes, for example on those stainless capped 19mm lugnuts that ford used to use a lot, which often rusted and swelled up so the correct socket would no longer fit.
I have a 23mm wrench that I've used the sum total of once, on the oil pan bolt on an older Volvo, most have 24 so this one must have been an oddball.
Same story with 25, 26, 28 and 29mm which are very rarely seen, but i have sockets and wrenches for.
28mm does turns up on some hydraulic and air brake systems, and is coincidentally very close to 5/8 whitworth...