Most of the time when I put multiple package statements in the same file, I do that to show a specific behaviour. To explain something, or to show a bug. Like a posting to Perlmonks or usenet. Or on a mailinglist. ;-)
Well, my response was more motivated by the comment "yeah but Perl Best Practices says you should do it".
So why does Perl Best Practices say it? I don't know. As I said I don't have the context to see exactly what TheDamian was saying. Basically I dont think it is "best practice" to do this. It is a good idea when multiple packages are in a single file, but its of minimal value when you only have one, and in that case IMO is actually bad practice as it increases indentation with no benefit.
My guess based on the quoted text is that TheDamian meant the case of multiple packages in one file and not a general advisory. Which just says that taking PBP quotes out of context isn't so wise.