There are a lot of IPs which got both movies and shows. Linking these would help useres to quickly discover these media which is stored in different libraries.
One request for it was closed but I don’t think that the given solution is satisfying:
In my opinion this is a hacky way to kinda get this result by creating collections in both libraries with the same name. This works well for IPs with many entries like Star Wars. But for for IPs like Firefly this means creating one collection in movies with one entry (Serenity) and a collection in Shows with one entry (Firefly).
When you create collections for all desired links this clutters all of the collections sections and reducing the usefulness of collections big way.
Also the it’s tedious and error prone because the collections have to be named the same, rename one collection you won’t notice any broken linking.