A link node is a connection from one WellSpring Project to another.  They are used when you want to create large consolidations, yet want to manage the data in smaller blocks.   They add significant performance advantages over calculating thousands of wells every time you need to get a business unit summary .  They can be included in any project, and the flow from a linked nodes moves through the network in the same way as any other  source node (well).  

Often existing production (base production) wells are placed in a separate project, and then the existing production project can be linked to many development option projects or scenarios.