My attitude toward punctuation is that it ought to be as conventional as possible. The game of golf would lose a good deal if croquet mallets and billiard cues were allowed on the putting green. You ought to be able to show that you can do it a good deal better than anyone else with the regular tools before you have a license to bring in your own improvements.
-- Ernest Hemingway, Selected Letters
Punctuation is an area of writing that is not always taken seriously, even by those who are experts on it. It is not a particularly glamorous or even interesting part of composition. No debates rage over it. No journals devote much attention to it. No working professionals spend their time wishing they could master it. In short, it is usually treated in the way Harry Shaw suggests in his foreword to one of the few book-length treatments of modern punctuation:
Punctuation and spelling apparently cause more people more trouble than any other aspect of writing with the possible exception of what is loosely known as "grammar." Both are somewhat mechanical and superficial phases of writing, not nearly so important as having something significant to say and a genuine interest in saying that something, whatever it is. 1
Yes, punctuation does cause people trouble. And it is mechanical. However, it is not superficial. Effective punctuation powerfully affects what the writer says, and questions about punctuation are almost always questions about the writer's meaning.
Effective punctuation also contributes to the writer's construction of ethos in several ways. First, it promotes the clarity of the writer's ideas, and this will help to show that the writer is in control of the material and able to communicate. Second, it demonstrates that the writer is familiar with literary conventions taught as part of a formal education. Third, it shows that the writer is willing to follow these conventions, as one might follow other conventions in our society, in the interest of providing the reader with shared meaning.