Update event-overview.md

Author: t-vnamani

articles/governance/policy/concepts/event-overview.md

@@ -17,17 +17,48 @@ Critically, you only pay for what you use.
 
 Azure Policy events are sent to the Azure Event Grid, which provides reliable delivery services to
 your applications through rich retry policies and dead-letter delivery. To learn more, see
-[Event Grid message delivery and retry](../../../event-grid/delivery-and-retry.md).
-
-The common Azure Policy event scenario is tracking when the compliance state of a resource changes
-during policy evaluation. Event-based architecture is an efficient way to react to these changes
-instead of scanning the compliance state of resources on a fixed schedule.
+[Event Grid message delivery and retry](../../../event-grid/delivery-and-retry.md). Event Grid takes 
+care of the proper routing, filtering, and multicasting of the events to destinations via Event Grid Subscriptions. 
 
 > [!NOTE]
 > Azure Policy state change events are sent to Event Grid after an
 > [evaluation trigger](../how-to/get-compliance-data.md#evaluation-triggers) finishes resource
 > evaluation.
 
+There are two primary entities using Event Grid: 
+- Events: These can be anything a user may want to react to – includes if a policy compliance state is
+   created, changed, and deleted of a resource such as a VM or a file in storage.
+- Event Grid Subscriptions: These are user configured entities that direct the proper set of events
+   from a publisher to a subscriber. Subscriptions can filter events based on the resource path the event
+   originated from as well as the type of event.
+  > Can choose scope: Azure subscription and Management group 
+
+The common Azure Policy event scenario is tracking when the compliance state of a resource changes
+during policy evaluation. Event-based architecture is an efficient way to react to these changes
+instead of scanning the compliance state of resources on a fixed schedule.
+
+Another scenario is to automatically trigger remediation tasks without manually ticking off 'create 
+remediation task' on the policy portal page. Event Grid checks for compliance state and resources that are currently 
+non-compliant can be remedied. Learn more about [remediation structure](../concepts/remediation-structure.md).
+  > Remediation requires a managed identity and policies must be in Modify or DeployIfNotExists effect. [Learn more about
+effect types](../concepts/effects.md).
+
+The last scenario to consider is to use event grid as an audit system to enforce configurations to 
+store state changes. This can be helpful to understand to check reason for non-compliancy over time.
+
+## Event Grid Benefits
+Event Grid has a few benefits for customers and services in the Azure ecosystem: 
+- Automation: Event Grid provides an automated way to trigger tasks and alerts based on compliance events
+- Latency: Event Grid aims to deliver policy events with sub-second latency meaning services and user
+applications can react to policy compliance events in real-time.
+- Durable delivery: Each message is promptly delivered by Event Grid with a 30 second default delay and 
+  least once for each matching subscription. Event Grid retries transmission of an event if a subscriber's endpoint
+  fails to acknowledge receipt of it or if it doesn't, according to a predetermined retry schedule and retry policy.
+- Custom event producer: Event producers and consumers need not be Azure or Microsoft services. Leveraging Azure
+  Policy Event Grid, a change in a resource tag can trigger an Azure Function or the creation of a new storage blob
+  can trigger custom commands through service bus, or the control messaging on who responds to the state change. 
+  > Any 3rd party service can onboard Policy Event Grid as a publisher of events or can consumer events be pushed to Event grid. 
+
 See
 [Route policy state change events to Event Grid with Azure CLI](../tutorials/route-state-change-events.md)
 for a full tutorial.