The comma is a very useful punctuation mark enabling the writer to make their point much more clearly and avoid confusion. I have read passages where, due to the lack of a comma, the meaning was ambiguous.
I do not have hard-and-fast rules for commas. My guiding principle is to ask myself whether it adds to the clarity or the rhythm of the sentence. Typically I use them to separate ideas or lists of objects or, in the case of a long sentence, insert parenthetical remarks, as I just did.
But there are others who overdo it, as in the passage below. (Ignore the various typos and spacing errors because this looks like it was written in a rush and not proof-read before printing.)
Well,I decided to get up early,at my central London Hotel, and walk,my dog,until breakfast time.
No sooner had I got out the holtels front doors, my dog ,got spooked by the door man,and consequently, I stopped in my stride, causing the young man behind me ,to bump in to me.
Obviously I immediately opologized,and said” sorry my dog got spooked.
The guy bend down,to say hello to her,and she was taken by his kindness.
Most of those commas are unnecessary and make the meaning more obscure. Here is my rewrite, where I have eliminated eleven of the fourteen commas.
Well,I decided to get up early at my central London Hotel and walk my dog until breakfast time.
No sooner had I got out the holtels front doors, my dog got spooked by the door man and consequently I stopped in my stride, causing the young man behind me to bump in to me.
Obviously I immediately opologized and said” sorry my dog got spooked.
The guy bend down to say hello to her and she was taken by his kindness.
Much clearer, no? Definitely a case where less is more.