It's a common requirement to provide extra info about the context of the assertion. For instance one might want to include values of local or dynamic bindings into the assert report, or use clojure.spec/assert to leverage structured errors with {{specs}} outside of testing environments.
With {{clojure.core/assert}} one can splice extra data into formated message but with {{clojure.spec/assert}} there is no such feature. The {{message}} argument to clojure's {{assert}} was added in CLJ-774, and it was acknowledged there that the mechanism is not ideal. One notable benefit of passing reports as data is that editors can handle those gracefully in case of large data.
This proposal is related to CLJ-415 but has a broader scope. With an extra map one can pass any value (not just locals), and there is no danger of inadvertently flooding the REPL with large locals.
