I'd like to know whether or not the following examples are correct in relation to comma usage with independent/dependent clauses.
Every time I come across examples to use commas in separating independent clauses with a comma, it follows a pattern such as "He read the book, and he really enjoyed the penultimate chapter." I don't have trouble with this one.
Then I see examples, in published works, such as "They appear in groups, and are multiplying rapidly." Is leaving out the "they" between "and" and "are" just for the sake of reading with a better flow or something? Should it have just left out the comma?
"He was ready to lead everyone to safety, and victory against X". Without the comma, would it be to suggest "safety against X" as well? Hence, is it why a comma would be necessary in this case? Is it then treated as a "list", so to say?
So, in the cases of "They appear in groups, and are multiplying rapidly" and "He was ready to lead everyone to safety, and victory against X", are they both okay to use? Or perhaps the former is simply not, but the latter is necessary in such context?
Thanks for the help! I really appreciate it! (Racking my brain with commas - trying to edit a huge piece of work).