Selecting multiple objects and giving them all the same tag (or relation in general) at once.
Adding a relations option to the action menu when selecting one and multiple objects
You have 10 bookmarks about receipts you wanna cook. Instead of opening every single bookmark and tag it with “receipt” you can simple select all objects/bookmarks and give them all the same tag with one action.
Tagging multiple objects at once would be already a huge deal. No need to implement a multi action for all relations.