Why use a custom module instead of a clock divider?
It's all about the context of the larger application. "Clock divider" implies to me that the output will also be used as a clock, or maybe a clock enable signal. "Preamble generator" implies that the output will be used as data. This is a fairly trivial example, but in more complex projects, meaningful names can go a long way toward making a design understandable to another person.