When you get an Office 365 license you also receive a free Azure tenant. This Azure tenant only generally has a single service enabled. That service is Azure Active Directory.
You do not pay for this, it is included with your Office 365 subscription and here’s how you are able to view it:
The Azure tenant that you get with Office 365 won’t unfortunately provide you with access to other Azure services (such as Virtual Machines) out of the box but it can. The way that you enable this existing Azure tenant for other Azure workloads is that you now add a paid Azure subscription.
Thus, when you add a paid Azure subscription into an Azure tenant created by Office 365 you now get the ability to access all the Azure services (like Virtual Machines, Backups, etc.).
What I suggest is that when enable an Office 365 tenant you should also immediately add a paid Azure subscription. The reason I say that is that Azure billing is handled differently to Office 365.
Office 365 is a flat fee per month based on the user count in the tenant. Azure however is a consumption based pricing model generally. This means, you don’t pay for Azure services until you start using them. Thus, enabling a paid Azure subscription into you Office 365 subscription is not going to cost you anything until you start actually using Azure services.
Adding a paid Azure subscription immediately gives you the flexibility to spin up Azure services immediately when you need them instead of having to wait for the subscription to be provisioned. It means if you need a temporary server or some cloud backup then you can configure and start using that service immediately, no waiting as the tenant and services are ready to go.
So with an Office 365 tenant created and a paid Azure subscription in place what are most likely first Azure services you should consider? I’d be looking at Azure DNS to host the name server records for Office 365, a site to site VPN back to on premises infrastructure, Azure SMB Files and then probably Azure Backup and Site Recovery. The choice is yours and with the paid Azure subscription in place you can run these up whenever you need and feel assured that you’ll only be billed when you actually start using them.
In short, think of Office 365 and Azure together. This means they should be deployed together as there is no financial reason not to in my books. With both deployed you’ll be in a far better place to respond to whatever the needs of the business are.