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There are several advantages to using Resource Manager. The deployment is faster because resources can be deployed in parallel rather than sequentially as they are in ASM. The Resource Manager model enables each service to have its own service provider, and they can update it as needed independently of the other services. Azure Storage has its own service provider, VMs have their own service provider, and so on. With the ASM model, all services had to be updated at one time, so if one service was finished and the rest were not, the one that was ready had to wait on the others before it could be released. Here are some of the other major advantages to the Resource Manager model:

Deployment using templates
 You can create a reusable (JSON) template that can be used to deploy all of the resources for a specific solution in one fell swoop. You no longer have to create a VM in the portal, wait for it to finish, then create the next VM, and so on.

 You can use the template to redeploy the same resources repeatedly. For example, you may set up the resources in a test environment and find that it doesn’t fit your needs. You can delete the resource group, which removes all of the resources for you, then tweak your template and try again. If you only want to make changes to the resources deployed, you can just change the template and deploy it again, and Resource Manager will change the resources to conform to the new template.

 You can take that template and easily re-create multiple versions of your infrastructure, such as staging and production. You can parameterize fields such as the VM name, network name, storage account name, etc., and load the template repeatedly, using different parameters.


Resource Manager can identify dependencies in a template but allows you to specify additional dependencies if necessary. For example, you wouldn’t want to deploy a virtual machine before creating the storage account for the VHD files that are used for the OS and data disks.


Security
 You can use the new Role-Based Access Control (RBAC) to control access to the resources in the group. For example, you can assign the Owner role to a user, giving that user full administrative privileges to those resources in the group but not to other resources in the subscription. Other roles include Reader (you can read anything except secrets) and Contributor (you can do most anything except add or revoke access).


Billing
 To help organize all of the resources in a subscription for billing purposes, you can assign tags to each resource and then retrieve all of the billing information for a specific tag. For example, if one department owns a web application and several related components, you can assign the same tag to all of those resources. Then, you can retrieve the billing for that department by retrieving the billing for that tag.

Source of Information : Microsoft Azure Essentials Fundamentals of Azure Second Edition