Ferrer made his mark in many ways but is most often recalled as the lyricist of several of Astor Piazzolla's most famous works in the late '60s and early '70s, including:
Even in its early days of the late 19th century, singing bore a function of most any other folk music: storytelling through song after a long day. Much has changed since those early days in the conventillos where improvising over a habanera rhythm was the extent to which a vocalist was involved- certainly not arranging lyrics to an orchestral setting.
Few had a better understanding as to arc of a song's presenter, subject matter, manner (or even place) in which it was told, than Ferrer. This might have been the case as far back as 1959 with his book 'El Tango: Su Historia y Evolucion' but certainly must have been cemented by his gigantic 3-volume tome 'El Libro del Tango, Arte Popular de Buenos Aires'.
'...And besides, the tango is one of the few song-forms in this century that undertakes not only a lyric excursion but a reflective one as well. The tango thinks. The tango thinks about the truth without claiming to modify it. It simply meditates upon it, which is also part of poetry."