Compare these two sentences.
He stole a hat and a coat.
He stole a hat and coat.
In the first sentence and links two noun phrases (a hat, a coat); in the second it
links two nouns (hat, coat). The second sentence suggests that there is a link
between the two items, that they belong together.
He stole a hat and a typewriter. (not linked)
He stole a cup and saucer. (belonging together