” Motoko provides numerous features to help you leverage this environment, including language features that allow your heap to self-migrate when you upgrade the software of a canister.” https://sdk.dfinity.org/docs/language-guide/motoko.html

So in this sense it could be a bit like creating migrations to your database. Maybe on ”cloud scale” you just would like to migrate the data when it is used.

Edit: Few more details in this document: https://sdk.dfinity.org/docs/language-guide/actors-async.htm...