git-version-gen doc: writing to intermediate file

[Basil L. Contovounesios]

The commentary in build-aux/git-version-gen illustrates how the files
.version and .tarball-version could be generated:

  $(top_srcdir)/.version:
        echo '$(VERSION)' > $@-t
        mv $@-t $@
  dist-hook:
        echo '$(VERSION)' > $(distdir)/.tarball-version

I'm curious why one recipe writes a temporary file first, whereas the
other writes the target directly.  Is the distinction meaningful?

Is this specific to Automake, or perhaps a more general
security/portability consideration?

I'd appreciate a pointer if this is already documented somewhere - my
searches came up dry.

Thanks,
-- 
Basil