What good is literaracy (alone) without reading comprehension?

Being able to read road signs and the like?

I'd say that there can be degrees of reading comprehension, and I tend to view functional illiteracy as literacy attrition, kind of secondary illiteracy. I guess it's useful to distinguish it from strict illiteracy (somebody not having learned how to read in the first place), as it requires a different kind of treatment, even if the symptoms of both are similar.