Comment by c22
3 years ago
The way I was taught, you use the comma for a brief aside--em dashes are used for a larger diversion (and parenthesis are for the most tenuous connections.)
In other words a reader should be able to skip reading the contents of parenthesis with negligible impact on the context or meaning of the sentence. They should be able to skip reading the contents of em-dash-seperated text without changing the meaning of the sentence. And text between commas should be considered integral to the sentence, while secondary to the primary gist.
What you reference is that commas are used to set off non-restrictive clauses, where the meaning of the sentence is clear without the additional clause. Though, the non-restrictive clause provides additional description of a word in the main sentence.
Such as:
Sometimes writing for money, rather than for art or pleasure, is really quite enjoyable.
Other than that, many people have come up with many writing styles. We mostly seem to be able to understand each other, so we are "all good".