Conditional sentence: "If someone wants a crash course in a period of history, then watching a couple of documentaries will probably suit them better" uses a conditional sentence to specify the best choice for different learning needs, increasing the logic of the answer.
Comparative degree: "for a deeper understanding" Here, the comparative degree is used to emphasize the difference between deep learning and superficial learning.
Present participle phrase as an adverbial: "People only have the attention span to watch TV for an hour or two, so documentary makers need to squeeze in as much as possible" Using a present participle phrase as an adverbial describes the limitations of documentary production, increasing the amount of information in the sentence.
Contrast sentence structure: "Books though don't have this problem, and they can cover far more" By contrasting the advantages and disadvantages of books and documentaries, it demonstrates the differences between different media in conveying historical information.