Amendment: Perhaps it's debatable what "substantive benefit" would be, but writing the whole app in it is a huge benefit if you really want to do that. That is to say, for years people wanted to write Web UI stuff in various languages, this also allows for that.
So while the concrete performance boost may not be meaningful in writing an entire web app in C, Rust, Go, Python or w/e - to the developer happiness the boost may be huge for those devs that want it.
My next app I'm planning on using a Rust WASM DOM framework, and I know there are some in Go as well. This is primarily for developer UX.
One example among many ramping up
As for designers, thank you for finding a much more diplomatic phrasing than the one I was about to write.
I should just have linked something done in Unity instead.
And thanks to many, including HN readership, Chrome and Safari are the only browsers that many businesses care about nowadays.
i.e. Figma said it reduced page load times by a factor of 3, though they were using WASM to replace existing asm.js code.
https://www.figma.com/blog/webassembly-cut-figmas-load-time-...