For personal computing (Windows) it is:
- Disconnected operation. Your laptop is still useful when the network is inaccessible.
- Performance. Local applications don't have to transfer data back and fourth over the network, and therefore can be much more responsive.
- Synchronized state. Your data and your applications are centrally managed, and they are up-to-date no matter where your access them from.
- Ease of deployment. An application on a website is deployed to millions of users who just need to follow a link to access it.
Maintaining synchronized state is a tricky problem in the programming models popular today, but the right framework can make writing "autosynced" applications easy. In combination with the framework for deployment similar to Java Webstart, a platform can offer the best of both worlds—"either or" trade-offs will become a thing of the past.