Adding or deleting commas is a good way to vary your writing. I’ve written on this before. (internal link) First drafts have too many commas. Revise. Be aware, though, of any change in emphasis (see below). Remember, too, that despite our desire to add or remove a comma, the first responsibility of a sentence is to make sense.
Before:
Once in office, Trump can quickly alter his Supreme Court agenda.
After:
Trump can quickly alter his Supreme Court agenda once in office.
Note the last word in the first sentence is agenda. And in the revised sentence the last word is office. You may elect to keep a comma if you think a particular word must be emphasized or used last.
More examples:
Later Sunday afternoon, demonstrators planned to assemble at Oakland’s Lake Merritt.
Demonstrators planned to assemble at Oakland’s Lake Merritt late Sunday afternoon.
In San Francisco, about 150 protesters congregated Saturday afternoon outside the Civic Center BART Station . . .
About 150 protesters in San Francisco congregated Saturday afternoon outside the Civic Center BART Station . . .
As participants assembled to march, a man walked by and jeered.
A man walked by and jeered as participants assembled to march.
Friday night in Oakland, about 100 people marching through downtown were monitored by police in riot gear.
About 100 people marching through downtown Oakland Friday night were monitored by police in riot gear.
