The grammatical label faḍlah does not mean useless verbiage. It refers to a constituent outside the core predicative structure, such as an appropriate adverbial or qualifying element. Such a constituent may nevertheless be crucial to the rhetorical value of the statement.
In tatmīm, the question is not whether deletion would destroy the bare syntax. Rather, one identifies the additional benefit supplied by the constituent. A statement can already be complete at the level of basic assertion and still be substantially enriched by a further qualification.