ProdParametersDim , is a table that hold the parameters by inventory dimension (by site).
ProdParametersDim::findDefault().RouteJournalNameId → this will give you the journal name assigned in the default parameters (with blank dimId)
ProdJournalName::standardJournalName(ProdJournalType::RouteCard); - this takes the production orders inventDim and return the journal name based on it (based on the site in the production order).
There will not be any difference with the result returned by these method, if you are not using production parameters by site.