I agree with Discipulus that you should document all your modules for those that must maintain them in the future (even if that is only you).
For advice on how to document your modules, see this recent general advice on documenting Perl code.
Update: Some further commenting and documentation tips from On Coding Standards and Code Reviews:
In reply to Re: documentation best practices for internal modules
by eyepopslikeamosquito
in thread documentation best practices for internal modules
by hotshoe
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