Upgrading? Re-installing

Yes, it left me a bit alarmed actually at first when I saw it described.

But it appears that what they're talking about as an "upgrade" actually flushes everything on
the system, and this is a feature which changes that to optionally not destroy /home.

So it's not like an ordinary operating system upgrade at all, it seems like it would be more
useful for "sidegrades", throwing away the OS but keeping the data. I don't know if that means
Ubuntu doesn't provide a mechanism for routine "same OS, newer version" upgrades, or just some
users don't like the potential for build-up of "cruft" (e.g. after five years of Red Hat
upgrades I had some obsolete binaries in /usr/bin/ that were so old my kernel wouldn't run
them, but the package manager had never actually deleted them)

Personally I've been very happy with upgrades of Red Hat and Fedora on multiple systems over
the years. They haven't always worked smoothly, but they were definitely less painful than
re-installing everything.