We do, but not exclusively. Otherwise, it may get boring.
So our read alouds and my daughter’s independent reading books do reflect the period of history we’re studying. But I add in other random books to liven it up. We’ve done some war themed books, so we’re reading an Oz book right now. Variety is the spice of life. And even I get tired of reading so many books on the same topic over and over.
Advantages — we learn through repetition. So my daughter reads the same concepts in several formats and it is reinforced. Sometimes one book explains something better than another. Often historical fiction gives a better view of history than a mere factual recounting.