This is switch that changes inputs depending on if the Nuke script is rendering or not. The logic is based off the $gui and nuke.exectute() functions. I originally made this to help manage heavy DOF/Vector nodes in my own comps, but after becoming a supervisor, and dealing with a bunch of “Broken scripts” that turned out to just be forgotten $gui expressions, I decide to share it with my teams. You can read more about this node here 

The RenderSwitch can be used in either $gui or nuke.exectute() modes. $gui is very reliable, but only works on a render farm, and is the default mode. You can switch it to use nuke.execute() instead, which will work locally, and on the farm, but please keep in mind that this mode is much less reliable depending on what version of nuke you are using, and if you have any custom tools running render/execute cmds, it may not switch inputs as expected