One of the characteristics of cloud computing is agility. Agility means how rapidly you can provision cloud resources and how quickly you can change to meet a scale need. In the context of infrastructure provisioning, you sometimes choose a wrong VM size for your application. Another case when the changing need exists is to scale down the infrastructure when you want to release resources. Saying your e-commerce only needs to be boosted during a specific marketing campaign. After the campaign ends, you need to change the size back to origin to save cost.