It helps readers hear you the way you want to be heard. Don't let the rules scare you. For they aren't hard and fast. Think of them as guidelines. Use your own common sense, remembering that you can't expect readers to work to decipher what you're trying to say.
Punctuation puts body language on the printed page.
Show bewilderment with a question mark, a whisper with parentheses, emphasis with an exclamation point. The tight, closed structural system, which hews closely to the sentence's grammatical structure. Most writers use a little of both. In any case, we use much less punctuation than they used 200 or even 50 years ago. If you have to struggle over commas, semicolons and dashes, you've probably built a sentence that's never going to fly, no matter how you tinker with it.