Organize and lay out objects with collections
Object Bar
An Object Bar is a dynamic collection of objects positioned in a horizontal or vertical stack. Spacing between objects can be configured. This component is usually used to format UI, such as a button bar, but in this example we will use it to position pieces of a model.
Difference between Prefabs and Collections / Object Bar
Collections are only used for organizational purposes. Any changes made to a game object in a collection aren't reflected in other game objects. They're entirely different from Prefabs because they're only used to arrange a group of objects in a specific order.
Prefabs, on the other hand, are assets that assist in propagating new changes to all its instances. Prefabs are a reusable set of objects arranged in a particular way, but any changes made to the game object in a Prefab are reflected in all of its instances.
Unity Canvas Positioning
While the Object Bar provides a tool to position objects for this specific use case, for most cases in MRTK3, object positioning should be accomplished with Unity's Canvas UI.