Here is a compilation I've made addressing 'comma usages which aren't necessary to police syntax but are still useful'.
Commas: Pauses, Shifts and Contrasted Coordinate Elements: write.com
Pauses
Any comma essentially represents a pause – one that gives your readers
the signal to take a quick breath before continuing with the next
portion of the sentence. When a comma is used, it places more emphasis
on what immediately precedes and follows the comma. Sometimes, there
is no grammatical rule [sic, with the narrow sense of 'grammar' sensibly used on ELU] that dictates the use of a comma in a
particular spot within a sentence, but the use of one, creating a
pause, can create an emphasis that does not exist without the comma.
Consider the following examples:
Example 1: Yesterday, I experienced the worst day of my life.
Example 2: The novice guitarist was butchering my favorite song, quite
badly.
In both examples, the comma is 'grammatically' unnecessary. It does,
however, create a pause that places more emphasis. In the first
example, the emphasis of the sentence shifts from “worst day of my
life” to “yesterday” and “I.” In the second example, the emphasis is
placed on “butchering my favorite song” and “quite badly.” You might
do this to emphasize the extent to which the song is butchered.
It is important to consider the overall meaning you are trying to
convey with a sentence when adding a comma as a pause to emphasize
something, as putting a comma in the wrong spot can alter the meaning
of your sentence.
[John Lawler comments on this correlating of pause and punctuation used in dialogue:
This is dialog, not text. Use a comma or a period or whatever seems to recreate the voice.] –
Shifts
Sometimes sentences require your readers to shift gears in a sense.
You might make a statement and look for confirmation by turning the
sentence into a question. Similarly, a comma represents the shift from
one thing to another.
Example 1: You plan on watching the Super Bowl, right?
Example 2: Sometimes you might feel a little nervous in new
environments, even when you are a little excited at the same time.
Both examples above represent a shift in the sentence. Using the comma
clues your readers that the shift is about to occur, even when they
are not consciously aware of the shift happening.
Contrasted Coordinate Elements
Normally coordinate elements do not require the use of a comma, as
they are connecting similar items, thoughts or phrases. However, when
the elements are contrasting, a comma is necessary to notate the
contrast. See the below examples:
Example 1: She was happy most of the day, but sad by the end of it.
Example 2: She received a high mark on the exam, not the low one she
expected.
Example 3: Her dancing partner was graceful, yet clumsy with certain
steps.
In each of the examples above, the part of the sentence that comes
after the comma contrasts the part that comes before it. Yet, both
parts are essential to convey the intended meaning.
I believe that this is all very sage and helpful advice: accuracy and disambiguation must have the first call on the resource offered by the comma, but judiciously using commas for other purposes where no conflict will occur makes good sense.
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One style guru has a recommendation that speakers might really appreciate:
One Woman Shop
Commas: Use commas to create a pause if your breath units are getting
too long.
Again, the caveat about the need for clarity trumps this.
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Another source gives examples where commas mirror pauses in the spoken word that would be needed to prevent misunderstanding:
UCalgary Eduweb _Punctuation 3.4J
Using Commas to Prevent Misunderstanding
Sometimes you must use a comma to make the reader pause in the
appropriate place in the sentence in order to prevent misreading.
Becoming a good writer means developing an awareness of how your
sentences will sound to the reader. Reading your work aloud, to
yourself or to a friend, is a good way to identify the places in the
sentence where pauses--or commas--are needed.
Example 1:
Without comma: Before leaving the soldiers demolished the fort.
A comma is needed here to prevent confusion in interpreting the
sentence. Without the comma, the reader might think that the soldiers
were being left, rather than doing the leaving. The sentence might
have gone on to end this way:
"Before leaving the soldiers, I kissed them all goodbye".
With comma: Before leaving, the soldiers demolished the fort.
Example 2:
Without comma: As she was rising to speak her mind suddenly played a
cruel trick and she forgot her speech.
Is she going to "speak her mind"? The reader is likely to read the
first part of the sentence this way, unless help arrives in the form
of a comma.
With comma: As she was rising to speak, her mind suddenly played a
cruel trick and she forgot her speech.
Example 3:
Without comma: Shelley having drowned Byron presided over the funeral
ceremonies on the beach.
Did Shelley drown Byron? If so, how could Byron preside over the
funeral?
With comma: Shelley having drowned, Byron presided over the funeral
ceremonies on the beach.
One final example:
Consider this question, asked by one zoo-keeper to another:
Without comma: Did the lion eat Fred?
With comma: Did the lion eat, Fred?
There is a crucial difference between the two sentences (especially to
Fred). Never underestimate the power of a comma!
