On powerpc64, powerpc64le and riscv64 some software wrongly assumes that
it runs on powerpc or riscv (32-bit).
One would be Perl's uname(): https://github.com/Perl/perl5/blob/blead/ext/POSIX/POSIX.xs#L3349. This causes e.g. OpenSSL's build system to be explicitly told what architecture to build (see security/openssl port).
Another would be Firefox's generation of default UA: https://searchfox.org/mozilla-central/source/netwerk/protocol/http/nsHttpHandler.cpp#931
I'm pretty sure there are others, it's just that powerpc and riscv are not that widely used. It also benefits armv*, since with this change either armv6 or armv7 should be printed, instead of plain arm