I doubt many people learn it anymore. Nowadays "rafters" are seldom cut, having been replaced by stamped together trusses. My Dad could cut every hip, jack and common rafter for a house just by knowing its' dimensions. They would be stacked up and ready for the guys to nail on. Never a measurement taken up on the roof. Vanishing breed I'm afraid.
I suppose so. Prefab trusses are sure a lot faster, and speed seems to be the main thing these days in construction. On the other hand, my old house, built in 1954 was done the old-fashioned way, and it's still square. My in-laws house was built in the 90s and isn't.
My projects are always small scale. The largest thing I've ever done was a 2-car garage. But I did the whole thing myself, from pouring the slab to roofing it. I learned a lot on that project. One of the principal things I learned was that raising a 24-foot long stud wall by yourself is not all that easy. Darned things wiggle. [grin]
There are a few builders left in my neck of the woods that know how to properly "cut in" a roof. The younger framers will stick an entire roof out of 2x6's, regardless of span (sheesh), cutting rafters one at a time. Sadly, our building inspection department doesn't take the time to check span tables.
Personally, I'm a Smoley's fan.