As in all book design, the style of these chapter heads is purely dependant upon the type of book. Novels are often supremely simple, usually denoted with just a number. Memoirs and Teaching books often have a little more hierarchy, with a main chapter title, a smaller subtitle, and then perhaps a quoted saying or scripture. Those levels needs an appropriate design, and preferably one with some flair, either classically so, or with some extra design attributes, such as in the associated graphic here. Beyond chapters, books of further levels of structure may be split into Parts, which additionally require styling. All this is considered from editor through to typesetter with Zaccmedia.