I think some of us have gotten the wrong idea about this concept of "two or none."
There are many, many places where one single separating is perfectly correct.
...If you call tomorrow, I will be here to chat.
...She was an arrogant, conceited person.
...We moved to Houston, Texas.
One comma separates sentence elements. When we talk about "two or none," we refer to the times when one comma is inserted and it should have been two commas to surround the element or no commas at all because we do not want to use one comma to separate the two sentence elements.
...Are you saying then, that he has not held any job in the last year?
...He was in my opinion, just being lazy.
In these two sentences, one comma is NOT correct. We need a pair of commas around the element. A single comma is not correct.
...He left somewhat later, to go to a better job.
...They intended all along, to cash in on the opportunity.
Here we do not need two commas; we do not need any commas. And one comma is absolutely incorrect.
Happy punctuating!
Margie