Many render engines support the ability to load pre-cached "snippets" of scene files in place of another object in the scene, known as render proxies. The basic workflow is as follows:
1) The object to be rendered is exported to a special "proxy" file. It is translated for the renderer at this time, and the resulting file can be loaded directly by the render engine without any additional translation by the host 3D app.
2) A "proxy" object is created in the main scene, and the file created in step 1 is selected as the final geometry.
3) At render time, the "proxy" object is ignored and the renderer directly loads to cached objects from step 1 in place of the proxy object.
This has a number of benefits:
* The object has already been translated to the renderer, and does not need to be re-exported on every frame and test render after that. Useful for background assets such as a trees, cars in traffic, buildings, etc.
* As a result, the object does not need to be evaluated or even loaded with the main scene, saving memory and improving performance.
* It allows nesting of objects that would not be possible otherwise, such as a tree with particle-based leaves being cloned by a particle system. This is not supported normally in Blender, but in a render proxy situation the tree would already be cached out, and cloned into a forest as a single object.