This template was created to counteract a limitation of the Kartographer module, that being that nested routes would not be recognized by the plugin. This resulted in a clash with OpenStreetMap's policy of nesting route relationships to avoid handling too much data at once. As an example, long interstate highways are divided into sections at state lines both on Wikipedia and on OSM. If the state's relations on OSM are tagged with the associated state's Wikipedia article, a map will display as intended. However, the overarching route will not work as intended, since the tagged relation nests other relations. This template circumvents this by retrieving the data for a route's sub-pages by Wikidata query, based on a "part of" relationship.
All parameters of the Maplink template can be overriden or added. There is, as of right now, one parameter that doesn't fall neatly into this category; overriding the "id" parameter will override the id of the superroute; as an example, adding the parameter id=Q406204 will show the map for U.S. Route 1 as a whole.