A quick primer on the use of commas

I don't like to be the pedantic dork who constantly criticizes other people's grammar, spelling and usage errors.  I'm very conscious of them, yeah, but I understand that the overwhelming majority of people don't need to know, for example, the difference between "Uninterested" and "Disinterested."

But more than a couple times recently, I've had actual arguments with people who put real effort into language, about the specifics of comma use, why it matters, and what constitutes wrongness.

Commas do more than indicate a pause in speech.  They indicate a shift in thought, or a delineation of entities.  In that sentence, for example, the commas separate two different explanations of functions of the comma.

If I had written:

They indicate, a shift in thought or a delineation of entities.

Or:

They indicate a shift in thought or, a delineation of entities.

the sentence reads awkwardly, but the meaning is more-or-less retained.  But if I had written,

They indicate a shift, in thought or a delineation, of entities.

The sentence is unclear.  In that third sentence, it takes a conscious effort to rework your interpretation around the speed bumps of commas jammed arbitrarily into the line.

It's an entirely valid criticism to point out that a comma isn't necessary in that sentence at all.  The 'or' does the job perfectly well, from a computational perspective.

But if I do choose to put commas in the sentence, there are correct and incorrect, valid and invalid, places to put them.  There are ways to place commas so that they increase clarity and pacing, offer breathing space for the reader and aid comprehension.  It's also possible to over-complicate sentences by nesting commas together, so that the argument the sentence makes may be logically cogent but difficult to parse.

It's also possible to use commas in ways that actively hinder comprehension, or transform the sentence into nonsense.  And if you want to defend using commas that way, there are two ways you can go.

"I don't give a crap about how clear my writing is" is a valid argument.

"My comma use is justified because my meaning can be laboriously picked out by an obsessively attentive reader who wants to give my writing far more attention than the ideas in it merit" is not.