There can be no hard and fast rules about punctuation. Meaning must be your guide. Punctuation is an art and not a science. A sentence can often be punctuated correctly in more than one way. To clarify the meaning of the printed or written language, punctuation is used. "Well-planned word order requires a minimum of punctuation."
Punctuation Matters
Less punctuation calls for skilful phrasing to avoid uncertainty and to warrant exact interpretation. A rigid design or pattern of punctuation cannot be laid down, except in broad terms. The style you adopt must be consistent and based on sentence structure. If the use of punctuation does not clarify the text it should be excluded. The aim of punctuation is to bring out more distinctly the author's ideas and it should assist in reading and it must prevent misreading.
Spelling and Punctuation Matters
Image credit
Note the difference between:
I will tell you nothing, nothing, do you hear?
and
I will tell you nothing. Nothing. Do you hear?
(The first sentence sounds excited, the second much more determined and emphatic).
and between
Well, I should never have thought it. (A mere statement).
and
Well! I should never have thought it! (This expresses amazement).
and between
What do you mean? (A question).
and
What do you mean! (This expresses indignation).
Punctuation Matters
Image credit
Note the difference between
John the carpenter's son (i.e., Tom or harry, or whatever his name may be, the son of John the carpenter).
and
John, the carpenter's son (i.e., John, the son of the carpenter).
and between
The boys went home to the farm and their mother, and I went to Bloemfontein.
and
The boys went home to the farm, and their mother and I went to Bloemfontein.
and between
The queen, who was angry, cried: "Off with her head!"
and
The queen who was angry cried: "Off with her head!"
(In the second sentence it is implied that there were several queens, one of who was angry).
Punctuation Matters
Image credit
and between
He said: "James is right, and I agree with him."
and
He said: "James is right," and I agree with him.
and between
John said: "That is your fault!"
and
John said: "That is your fault"! (In the first sentence John expresses anger, in the second the person reporting John's speech expresses amazement at what John said).
The report on a competition quoted below is from The Observer. It illustrates the point we are making.
Source: EBH Joubert: English Grammar
https://www.gpo.gov/fdsys/pkg/GPO-STYLEMANUAL-2008/pdf/GPO-STYLEMANUAL-2008-10.pdf
@frieda