Woodworking measurement has two forms: lumber, which is notional, pre drying, shrinkage and rough handling, and cut, which is required to be beautiful. Sometimes, it isn't about feet and inches as much as "the same"
Plumbing is another example where imperial works and is even used in Europe. It doesn't matter that a pipe is 3", it may as well be called "type B", since all you care about is if it's big enough for the purpose (you look that up in building code) and if the parts match together. The moment you need to perform calculations is when imperial becomes a total PITA to use.
WDYM by minimum radius? Are you referring to the part of my post where I wrote that you just look it up in the building code (as opposed to trying to calculate it), or when actually designing where the pipe runs?
The intersection of both. I did a very bad job of plumbing an electric shower into my flat in York back in the 80s and working out how to route the pipe to meet both ends requirement of where I could connect it into supply, and where it had to be to deliver water to the heater, was massively confusing. I am sure a plumber would understand this innately, but I wasted 2+ m of copper pipe trying to "route" it, without understanding the limits of how I could bend it, or cut and use a fitting.
The building code(s) only get you so far. There's also aesthetics.
I made the mistake of watching (as a kid) a plumber use his own body to form the curves, and assumed "it's that easy" without taking in that he was 25 years past his apprenticeship and had bent thousands of pipes, and used a former almost all the time. It's a different game when its you, the pipe, and twenty needle-jets of water streaming out of the badly fitted olives, lack of PTFE (or too much) tools which don't fit, pipe with ugly crinkles in them, splits along the length...
