It depends on your goals and your circumstances, I suppose.
The idea of booting directly and anonymously from a basic, clean image, from a cryptographically trusted source, with nothing more than a connected device is powerful.
Ofc, you may rather have a local version on whatever media you wish, but I think the long term vision is to make local storage redundant.
IMO, a hybrid between the two would be pretty handy to begin with. That us, you use your local disk for caching, particularly for the OS. This would also allow write access for updates/patches.
Also note that with the likes of Ubuntu Snappy and other core only OS architectures, the image is small. In addition, apps are stand alone containers which can just plug in without concern for dependencies or Linux flavour. In short, the OS becomes just a vessel for isolated containers.
As Ubuntu Touch seems to be pursuing something similar and Ubuntu Snappy is following on, I can see how this would be a good fit with Safe net. All that would need to change is the distribution channel - from the internet to safe net.