What is the difference between Collections and Tags?

Tags vs. Collections: "Grouping content within the same object is done with collections. Grouping content from different objects is done with tags." Collections are well-suited for subcategories of an object type. For example, it makes sense to create collections for “Authors,” “Family and Friends,” or “Profession” within the object type “People.” Or for an object type “Sources,” collections for “Books,” “Papers,” “Articles.” Tags are good for topics, ratings or statuses that can be relevant to all object types. For example, status tags like #ToRead, #ToListen, #active, #inProgress or #waiting, or topic tags like #Psychology, #Sleep, #AI , #Skincare, or #MachineLearning.