The workbook follows the exact modular structure of the coursebook. A2 is typically divided into 12 modules (often split across two volumes: A2.1 and A2.2). If a student learns about "Health and Fitness" in Module 5 of the coursebook, the workbook provides immediate exercises for that same topic.
If you rely solely on the Kursbuch for the course, you will pass the class but struggle with the exam. The Netzwerk Neu A2 Ubungsbuch is not optional; it is the bridge between knowing German and using German.