Here's why:

* Animals: Glycogen is the primary form of carbohydrate storage in animals. It is stored mainly in the liver and muscles. When blood sugar levels drop, the liver breaks down glycogen into glucose and releases it into the bloodstream to provide energy for the body.

* Fungi: Fungi also use glycogen as their primary energy storage molecule.

* Bacteria: Some bacteria utilize glycogen for energy storage.

Note: Plants, on the other hand, primarily use starch for energy storage.