This plugin extends question bank navigation node with "Purge categories" item.

Select category you want to delete and specify where to move questions, that cannot be deleted. Questions, that cannot be deleted, are questions, that are used in quizes or in history of quiz attempts. Such questions will be moved to specified categories and marked as hidden.

This can be useful if you are importing a lot of questions with many categories and want to delete all of them and reimport them.