The handy Null SOP basically does nothing. It does no cooking and consumes no memory.
One convention that is often used in Houdini is the use of a Null node at the end of a node chain. This node is often called “Out” but you can call it “Waffle” if you want.
It’s handy because it makes it easy to pick nodes when you need to reference them from another network or another node such as an Object Merge. Assign it a color for even easier access!
Two options available for the Null SOP are
Cache Input and
Copy Input. The Cache Input will cache out the Null SOP‘s input but keep in mind this will consume memory.