As noted above seven hours before your comment ;) the purpose for this project is for embedding interactive WordPress installations in documentation and to provide a playground in the browser for testing code or learning how to write plugins, etc...
The forest is shrinking the time and distance between code we care about and visualizing the results. WASM and an in-browser environment is the tree. Even for experienced devs it's not always readily available to have a web server, PHP, a database, and WordPress running where you can quickly make a change and test it out or demonstrate it to others.
This makes it possible to ship a WordPress site as a demo site (with pre-filled content and structure) where anyone can show off their WordPress plugin or theme without needing to have a backend or worrying about securing it.