Along came Elastic Pool. Interestingly, Elastic Pools brought back the notion of a centralized compute shared across databases. Unlike on premise SQL Server on premise though, that compute doesn’t sit with the server itself but with a new resource called an elastic pool.
This allows us to provision certain compute, i.e. DTUs, to a pool and share it across many databases.
His example is using a large number of small databases, where the total load is never the sum of individual expected loads. Another reason to use a pool is for cross-database queries in Azure.