Unfortunately, more than once I've seen an (anti)pattern of methods being moved into a module to shorten a class definition. This anti-pattern can be fairly easy to spot.
- Do you have a module that only one class includes (or extends).
- Do you have a module that requires other methods to be defined on the class that includes it.
A better solution could be to extract a class that encapsulates a subset of the responsibilities. If the behavior is required in various classes then it's probably time to look at converting the class to a module.