A recognizer emits words it heard, often without reliable commas or paragraphs. Rule-based cleanup is deterministic: strip um, expand a spoken command, fix spacing around punctuation, apply a replacement table. You can read the rules and predict the output. That predictability is why rules are the right default for code identifiers and legal phrases you must not paraphrase. They fail on messy grammar that is still what you meant.
A local language model, reached at 127.0.0.1 if it stays on the machine, can punctuate and tighten prose that rules cannot. It is extra RAM and an extra failure mode: over-editing, delayed insert, or a rewrite that sounds unlike you. Cloud rewrite APIs add a second network hop for text that may already be sensitive. The honest stack is layered: recognition, then rules you control, then an optional model you opted into, running locally if privacy is the point of the app.