Outside of making something - it’s very useful for setting up a quick project.

Stackblitz did this with Node (aka their Web Containers).

You could make a new project very quickly and prototype an idea. When finished, download it off the browser and deploy it.

You can create a SaaS with fully private data on the client side while using both local operations and managing control via API calls.

Think of it like a mobile app, but for the browser.

A common usecase for offline-first mobile app situations is shared business logic, especially for validations. Being able to validate client-side and detecting issues without a server dependency is a nice boost to UX.