An example I can give:
I use WebAssembly for a few cross-platform plugins. E.g. An AR 3D rendering engine in C++ and OpenGL. With very little effort it is working in browser. No bespoke code, same business logic, etc. Saved a lot of time vs creating a new renderer for our web app.
For me it allows a suite of curated plugins which work cross-platform. The web experience is nearly just as nice as the native mobile and desktop experience. This in turn increases market growth as more of my clients prefer web vs downloading an app (which is a large blocker for my users). I also enjoy the code reuse, maintainability, etc, :)
Another:
This year Max Factor (via Holition Beauty tech) won a Webby award for in-browser AI and AR. This was used to scan a users face, analyse their features, advise them on what make up, etc, would suit them, after which the user can try it on. This would have been impossible without WebAssembly.
This tech is also used by another makeup brands beauty advisors (via WebRTC) to call a customer and in real-time advise them on their make up look, etc.
Is this tech necessary? Probably not, but it is a lot nicer than having to go to a store. Especially when we are all in lockdown :)
1) https://www.holitionbeauty.com/
2) https://winners.webbyawards.com/?_ga=2.215422039.1334936414....
3) https://www.maxfactor.com/vmua/