It produced a duplicate entry when listing the extractors with '--list-extractors' and generates noise in the commit log when generating the supported sites webpage (like in 09f355f73b)
It needs to know the channel and the title of the list, because the ids change every time you browse the channels and are attached to a 'VISITOR_INFO1_LIVE' cookie.
In this case, it looks rather harmless (since the conditions for --restrict-filenames should not change while a process is running), but just to be sure.
This also simplifies the interface for callers, who can just pass in the idiomatic None for "I don't care, whatever is the default".