Yeah `sls invoke local` works well for testing individual functions where you are mocking the specific inputs or triggers. But there are a couple of cases where it can become hard to use. For example, if you want to test a Lambda function that's invoked by an API that needs authentication. Or if Lambda A publishes to an SNS topic that invokes Lambda B and you want to test the entire flow.

To fix this SST will deploy your entire stack, and let you trigger the workflow live. So you can hit the endpoint just as your frontend would, or trigger the entire SNS workflow. Except all the Lambda function invocations will be streamed to your local machine and the responses will be sent back.

This approach allows you to get the best of both worlds. The speed on an `sls invoke local`, without having to mock anything.