Rotating Arcs function like one of those revolving doors you invariably get your coat trapped in - as one character, or group of characters, come in, another is pushed out. While this can happen on a character-by-character basis, it's much more likely the the writer will make use of a Cast Herd.
Rotating arcs that employ cast herds need to do so in a fairly specific way in order to be successful. [...] [tvtropes.org]