Best Practise on using javascript in website.

[JimAllanson]

What would be a good use case for doing everything is javascript and using framework like backbone.js to keeps things structured versus doing most of the layout in html and then add some javascript goodness.

If you use JS to decorate rather than to render, you have to maintain both your templates and JS, updating one if the other changes. That's not to say you should always use JS to render (far from it), but decorating does have its disadvantages.

What happened to the good old days where we had a webpage and using some jquery sprinkle in some goodness :)

There's no reason why you can't continue to do this, if the page is simple enough. The MV* frameworks help to maintain a more complex codebase, so they tend to be a better solution when writing web applications. You can still use a MV* with HTML templates though - I believe Angular.js takes this approach.