Blazor can also run in 2 modes:
1) server-side where the UI is controlled by a websocket (via SignalR) connection to the backend which processes all the logic. Developing complex interfaces becomes much easier because everything runs on the server and the distance between a database query and UI update is very short. Save the verbose JS->API->Backend layers of code.
2) client-side which uses cutting edge WebAssembly to run your app. The WASM version is getting smaller and faster with every release and isn't much bigger than your standard big SPA which also has megabytes of javascript these days. It has a great JSON library and can also support GRPC-Web now for easy RPC.
Copying a C# class to use as a DTO from a database entity is way faster than trying to worry about serializing to a JSON structure while maintaining all the fidelity (like dates, big ints, binary data, etc).
Another example is reusing business logic like validation for data input. Blazor lets you use a single layer of logic instead of using JS-based simple validation on the form and more detailed checks on the server.
We use it for internal business dashboards and devops management tools. The ability to inject & use existing .NET services is pretty incredible in terms of productivity. We now maintain a monorepository because of this reuse potential.
https://docs.microsoft.com/en-us/aspnet/core/blazor/hosting-...
Down side is scaling, but I mostly write B2B apps. And by the time you run into scaling issues in B2B SaaS someone's rich.