I was wondering about the use of separating fiction into "parts", similar to chapters but larger and spanning more text and using these to divide up books within a series. If I am unclear, refer to Miss Peregrine's Home for Peculiar Children, Book 2, Hollow City. In this series, the second book is divided into two sections: part 1 and part 2, as well as chapters.
I was wondering where this is done in various works of fiction. I assume within a single stand-alone book it should be fine, but would it still be fine within a series where not all the books are divided into parts that way, such as the Miss Peregrine's book series? How about for a novella? Is it more advisable to keep all the content in one main body than to divide it in a smaller text?