While it does depend on the purpose of your site, even in the purest examples in the "web app" category, I can think of very few sites that are guaranteed to be

While it does depend on the purpose of your site, even in the purest examples in the "web app" category, I can think of very few sites that are guaranteed to be absolutely 100% useless without interactivity. Certainly not as useless as a white screen. In most cases though, you should be able to present a pretty useful static page by default without too much effort.