Not silly at all. It can't run faster, as there is a maximum speed your machine could do this. Doing it in the background can't change this but it is non-blocking. Many threads won't always help speed it up, but it does get it off of the UI thread. For example, the browser process may be single threaded or already using all the available cores it can.

Asynchronous behaviours, including synchronising with the UI aren't free and all add overhead. Of course the benefit is that the app stays responsive to user input.

Some problems can be performed in parallel, but even if they can then it may slow them down. Orchestration isn't free and unless you can use more cores it probably won't help. I wrote a simple demo of this in .NET Core [0] for a book [1] (where I've written more on these topics, from a C# perspective).

It may not be intuitive to web developers, as the server is naturally blocking and async has a different effect on HTTP request/responses. Yet if you've done any desktop/mobile app work then you'll know it's very important to not do anything intensive on the UI thread. It's a pretty common mistake to make.

[0]: https://github.com/PacktPublishing/ASP.NET-Core-1.0-High-Per...

[1]: https://unop.uk/book