This task is useful when you have people entering a workflow through form automation and need to add them to multiple tasks in parallel. Unlike the Conditional branching task, the Splitter won't qualify anyone for any of the options of possible pathways through the workflow, but instead is meant to send someone into all pathways after it's been added.
One use case would be when a form submission triggers a workflow for an Assignment task but you also want the submission to begin a Delay task that sends an email 3 days after the person submits the form. The timing of the Notification task in this case doesn't wait for the Assignment task to be completed.