The following key points will give you more information about the App Service plan:

• When you scale up an App Service plan, it affects all of the applications within this plan in a matter of seconds, provided that you do not have to either change anything in the code or redeploy the application.
• When you notice that the use of your apps is decreasing, you can scale it down. Otherwise, you will be still charged for the pricing tier you have scaled up to because it has reserved a VM that's running in the background.