I have noticed that no matter what deployment method I use (Portal or ARM template) to deploy an Azure VM in my Azure subscription, I always get two additional VM installed by default. I have no intention of using OMS or Security Center for certain workloads I run on Azure but having these two extensions hanging in a VM looked weird to me. The reason is I never installed them in the first place.
As you can see in the below image MicrosoftMonitoringAgent & Monitoring VM extensions are installed after a VM has been provisioned.
Security Center Data Collection from Azure VMs
When you enable the Azure Security Center for your sbscriptions in Azure, by default data collection is turned on. This setting provisions the Microsoft Monitoring Agent (which explains the auto installed extension) on all Azure VMs in the subscription/s and any new VMs that you create. The Microsoft Monitoring agent scans for security related configurations and posts them into Event Tracing for Windows (ETW) traces. Also any event logs raised by the guest OS will be read by the the Microsoft Monitoring Agent and will be posted back to OMS.
In case if you are using the free tier of the Microsoft Azure Security Center, data collection can be disabled in the Security Policy as below. Enabling data collection is required for any subscription that uses the Azure Security Center Standard tier.
Once I disabled the data collection I got rid of the OMS agent being that has been auto provisioned in my Azure VMs. Also note that event though the data collection has been turned off, VM disk snapshots and artifact collection will still be enabled. However Microsoft do recommend to enable the data collection regardless of the security center tier your subscription is on.