Calculation Nodes & Networks are useful especially for automating table calculations (like financial planning, sales commissions etc.) with inputs from various data sources.
Briefly, this is what a Calculation Node
1) Reads all input tables from databases or from the output of a another node.
2) Validates all input tables.
3) Executes the assigned table function to generate output tables.
4) Validates all output tables.
5) Writes output tables to the configured data stores.
Most typical data store is the generic database as explained in article: Persistent Table Array
Calculation Nodes are also practical for the modularization of analytical table computations. You may add new nodes to an existing network (i.e. group of nodes) for further data processing without affecting the functionality of existing nodes.