update template benefits

Author: tfitzmac

articles/azure-resource-manager/templates/overview.md

@@ -2,7 +2,7 @@
 title: Templates overview
 description: Describes the benefits using Azure Resource Manager templates for deployment of resources.
 ms.topic: conceptual
-ms.date: 03/25/2020
+ms.date: 04/06/2020
 ---
 # What are ARM templates?
 
@@ -44,6 +44,12 @@ If you're trying to decide between using ARM templates and one of the other infr
 
 * **Authoring tools**: You can author templates with [Visual Studio Code](use-vs-code-to-create-template.md) and the template tool extension. You get intellisense, syntax highlighting, in-line help, and many other language functions. In addition to Visual Studio code, you can also use [Visual Studio](create-visual-studio-deployment-project.md).
 
+* **Preview changes**: You can use the [what-if operation](template-deploy-what-if.md) to get a preview of changes before deploying the template. With what-if, you see which resources will be created, updated, or deleted, and any resource properties that will change. The what-if operation checks the current state of your environment and eliminates the need to manage state.
+
+* **Extensibility**: With [deployment scripts](deployment-script-template.md), you can add PowerShell or Bash scripts to your templates. The deployment scripts extend your ability to set up resources during deployment. A script can be included in the template, or stored in an external source and referenced in the template. Deployment scripts give you the ability to complete your end-to-end environment setup in a single ARM Template.
+
+* **Testing**: You can make sure your template follows recommended guidelines by testing it with the ARM template tool kit (arm-ttk). This test kit is a PowerShell script that you can download from [GitHub](https://github.com/Azure/arm-ttk). The tool kit makes it easier for you to develop expertise using the template language.
+
 ## Template file
 
 Within your template, you can write [template expressions](template-expressions.md) that extend the capabilities of JSON. These expressions make use of the [functions](template-functions.md) provided by Resource Manager.