Michael Albinus <michael.albinus@gmx.de> writes:

> Well, non-essential is not checked for *all* basic functions. Its most
> important use is to prevent expand-file-name and file-exists-p from
> action. See function tramp-connectable-p, and its use in tramp.el and
> tramp-sh.el.

Thanks to clarify its usage.

-- 
Thierry