In 2c8 you can reuse objects. That means that you can place an object in a model and reuse the same object in other models. This means that you can view the same object from different perspectives in the business, where the object's relations and meaning might be different depending on what model you are viewing. Reusing objects also makes maintaining the models easier, since if you change the object in one place it will reflect in all places the object is being used.
An example where reusing objects is beneficial is when adding roles in the models. The role "Project Manager" might for example be included in different processes where it has different relations to different activities, while the description of the role is the same no matter what model it's used in. By reusing the role you gather all the information about the role "Project Manager" in one object, and can find information about the role from all perspectives of the business. You can for example find out that the "Project Manager" is responsible for the activity "Compile project status" and is consulted in the activity "Plan project timeline".
To reuse an object, place an object of the same object type in a model. Start writing the name of the object and select the title of the object you want to reuse.
If instead you want to create a copy of an object, where an object might be called the same thing as another one but should contain different information, read this FAQ: How do I create a copy of an already existing object?