There are some cases on the threshold that this can be useful for.
For example, let's say your Node application's requirements changed, and now you have to transform a set of five JSON objects to one JSON object, with some big arrays, indexing, and sorting required. The operation takes 10-100ms of cpu time, which isn't nuts, but with thousands of requests per second would normally be a catastrophe. If you can spawn a thread in this case you can save the day.