Find this section in some selected objects' transform node Attribute Editor.
Render Proxy
If you are using render proxies to manage your scene, use this option to set your render proxy as renderable so that it is rendered instead of your base geometry.
This is a per instance flag. Therefore, if you have five instances of your base geometry, and you only want to replace three of them with your render proxy, you can use this flag to set the three instances as Renderable.
Render proxies allow for more efficient renders. Using this flag, you can choose not to load and render complex geometry that you do not need in your scene.
For more information regarding render proxies, see Using render proxies in your scene.