This lets the reader know that the series is coming to an end. He also gave me four calling birds. Then he gave me three french hens. He gave me two turtle doves and a partridge in a pear tree. By establishing a parallel structure, the author of this carol, no longer needed to repeat the subject or the predicate.
Parallel sentences are both long and efficient.
They can be particularly useful as you outline a thesis at the end of your introduction. In any study of automobiles, you should learn about the clutch, brakes, ignition, fuel system, piston rods. As you decide whether to repeat articles, you will consider how much emphasis you need to establish the parallelism for your reader. In some passive sentences a preposition will follow the verb and introduce an agent for the action the verb describes. But passive sentences frequently do not include this prepositional phrase and become agentless.