Hi Per
One of the use cases for having an approval task is when a certification template is configured to request approvals

In my case, a manager reassigned a task to a colleague, who has rejected that task. Before accepting / finalizing the rejection, it came back to the original manager for a final approval of this change

There are other use cases which will generate approvals, for example with multiple approvals configured or any custom workflow implementing user approvals.
As a side note, any self service request also generates approvals, however this is not currently implemented in the Portal, and only available in the IG UI.
Let us know if you require any further info on this
Regards
Rinat