TL;DR:
- "almost fast as native code for web browsers” - in case you wanna do some expensive computing without a server
- "Compiling Existing Applications for the Browser" - port existing code into the browser (eg cpp apps)
Using webasm as a general purpose platform for the execution of untrusted code is also pretty interesting - this might be within server side code or non-browser desktop apps.
TL;DR: - "almost fast as native code for web browsers” - in case you wanna do some expensive computing without a server - "Compiling Existing Applications for the Browser" - port existing code into the browser (eg cpp apps)