Running fetch in a web worker
Jad Joubran

When you use a worker when data transferring data between the worker and the main thread the data will be copied. If the amount of data you send/get to/from the worker is big this will actually reduce performance

I would advise to not use this pattern UNLESS you do some heavy processing of the response of the fetch. fetch calls are non-blocking and it shouldn't matter much if you do it in the main thread or in the worker.