Why it matters when you are writing
The formulas count syllables and words per sentence. That is all they do. They cannot see whether a term is standard in your field, whether a pronoun has a clear referent, or whether two clauses are joined by an implication a reader can reconstruct. A methods section full of necessary polysyllables will score badly and read perfectly well to its intended audience, so treat a score as a prompt to look, not a verdict.
The things that genuinely slow readers are structural. Sentences that run past forty words without a landing point. Three subordinate clauses stacked before the main verb arrives. Nominalizations that hide the actor. Pronouns — especially “this” and “it” — whose antecedent is two sentences back. Fixing any one of these does more than shortening every sentence to the same length, which produces a choppy rhythm of its own.
Where readability has real stakes beyond style: grant applications read by non-specialist panels, lay summaries, abstracts that cross disciplinary lines, and any document a policy audience will act on. In those cases plainness is not a concession, it is the requirement. Reading a passage aloud remains the fastest diagnostic anyone has found — where you run out of breath is where the reader does.
