I love the idea of web workers. I struggle to find a use case that isn't limited by serialization/deserialization.

AFAIK, workers are strings in and strings out. Often serialization is the most expensive operation, so adding additional serialization/deserialization steps can decrease performance overall.

The only use case I can imagine that would really benefit is computation-heavy with minimal input/output.

Until there is safe shared memory (please correct me if I'm wrong) I don't see many compelling use cases for web workers.