In better way to explain it. I have a project with a lot of details but also a lot of duplicated objects. It took a lot of time just to calculate for rendering and in some computers it showed me 'out of memory' message in 32GB RAM computer. I used CPU render method and all duplicated objects was using 'Alt + D' so it should use same source to avoid wasting memory. I don't know if it would help to append objects all to make groups? any other ideas to handel projects like that?
Mode: Object Mode
Panel: Tool Shelf ‣ Tools ‣ Edit ‣ Duplicate Linked
Menu: Object ‣ Duplicate Linked
You also have the choice of creating a Linked Duplicate rather than a Duplicate; this is called a deep link. This will create a new object with all of its data linked to the original object. If you modify one of the linked objects in Edit Mode, all linked copies are modified. Transform properties (object data-blocks) still remain copies, not links, so you still can rotate, scale, and move freely without affecting the other copies. Reference Expl. Duplicate Example for the discussions below.
Note If you require the applied material to not be linked you will need to turn on "Object" data on the material panel here.