Azure is built to give the end user the flexibility to choose the environment which they want to deply and manage. Where customers choose to manage the base operating system running the SQL database service and have complete administration of the SQL server, they can choose the option of deploying SQL server inside a Azure Virtual machine offering. This is part of Azure Vitual Machine (VM) offeringss. While this gives the flexibility to manage the complete OS and DB server environment, it has operational overheads of managing patches, upgrades, performance and backup of the data.
SQL PaaS has none of the above-mentioned overheads, but gives customer control over the specific Database instance subscribed. Microsoft covers the management of Infrastructure and the database server instance that hosts the database.
Partners can choose to use the Elastic pool option within PaaS to pool multiple databases of customers and choose to resource share based on demand of each database. This helps in scenarios where the resource requirements for the database is unpredictable.