You don't have to put different packages in different files, only when you need to make them available to use from other files. SOAP::Lite comes to mind as a module where it exhibits much different behavior depending on what's needed (eg, do we use 'xsi:null' or 'xsi:nil' for this version of XML Schema?

SOAP::Lite might be a bit of an extreme example, as they pack a *lot* into one file. (I count 28 package declarations currently, and it looks like more might be dynamically generated; I remember bugging BareBones Software for *years* about marking packages in automatically generated list of functions so that I could use it to find my way around the file).