Possible use cases are:
Execute graphs in chain
For example, we have to execute graph B, only if another graph A finished without any error.
So there is a relation between these graphs.
We can achieve this behavior by creating a graph event listener.
We create a listener for
graph finished OK event of graph A and choose an
execute graph task type with graph B specified for execution.
If we create another listener for graph B with the
execute graph task with graph C specified, it will work as a chain of graphs.