While high volume multi-tenant "customers/users/accounts" systems are common, they are not the only ones which benefit from sharded persistent stores.

For example, consider a system which monitors farm equipment for Caterpillar and John Deere. Lets say each company has 100k devices which send one message per day to the system.

While it is easy to envision sharding device messages based on "DeviceId / Company" in this hypothetical system, there would be no value sharding the two customers.