I never used git-new-workspace, so I don't really understand what you
describe here.
He describes a situation just like mine: even if I spend all day hacking
on nothing else than Emacs, I end up frequently switching between at
least 2, often 3 different "projects", which are simply 3 different
branches ("lightweight checkouts", actually, in Bazaar speech) of Emacs
(typically, "master", "local-work", and "emacs-24").
So for him (and for me) "multiple projects" is the norm, not
the exception. And indeed, I rarely used the etags facility for that
very reason: it all too often brings me to the file in the wrong branch.