When learning multiple foreign languages, would it be worthwhile investing time into mastering modern grammar theories (generative grammars, construction grammars, etc.) or are those too theoretical for practical use?
I will be particularly interested in the study manuals for specific languages, explaining grammar in theoretical terms (as opposed to the conventional descriptive grammar approach).
Example: Here is one such book that I found Foundations of French syntax by Michael Allan Jones (Cambridge University Press, 1996). This seems to be a grammar aimed at advanced learners of French which in the same time may serve as an introduction to transformational generative grammars as applied to this language (rather than usual English).