Have you experimented with single page web application, i.e. where the browser only \'GETs\' one page form the server, the rest being handled by client side javascript code (one
I call these single page apps "long lived" apps.
For "simpler applications" as you put it it's terrible. Things that work OOTB for browsers all of a sudden need special care and attention:
Note I'm not saying you can't do these things with single-page apps, I'm saying you need to make the effort to build them into the app code. If you simply had different resources at different urls, these work with no additional developer effort.
Now, for complex apps like gmail, google maps, the benefits there are:
One concern with long-lived apps is memory leaks. Traditional sites that requests a new page for each user action have the added benefit that the browser discards the DOM and any unused objects to the degree that memory can be reclaimed. Newer browsers have different mechanisms for this, but lets take IE as an example. IE will require special care to clean up memory periodically during the lifetime of the long-lived app. This is made somewhat easier by libraries these days, but by no means is a triviality.
As with a lot of things, a hybrid approach is great. It allows you to leverage JavaScript for lazy-loading specific content while separating parts of the app by page/url.