In 2c8 Modeling Tool, you can either reuse an object with the same title as an already existing object or create a duplicate of an object with the same title as an already existing object. This option pops up when you place an object and label it the same as an already existing object in your repository.
If you reuse an object, it means that the same object with the same ID can exist in multiple models in your repository. This means if you change the data on the object in one model, the changes affect the same object in other models. This way, you only need to update information on an object in one model.
If you create a duplicate of an already existing object, the objects will have the same name but different IDs. This means that the objects do not affect each other. You can therefore add or remove data from one of the objects with the same name without affecting the other object.
If you are uncertain if an object is a duplicate of another object or a duplicate of another object, you can compare the objects' IDs. You can do this by right-clicking the object and choosing "Properties" - "ID and permissions". If they have the same ID, the object is reused. If the have different IDs, the are duplicates of each other.
You can read more about the function "Reuse" in this FAQ: What does it mean to reuse objects?