There is a ton of unbelievably bad web code out there.
jQuery is a great example of a 'huge' and popular slowdown for a minor gain.
Sure, it's 'worth it' because nobody cares if a web app takes 1/2 second to render, but as soon as you trade speed for anything else you quickly end up with code that's as slow as your willing to live with.
Having said that there are a few modern web-apps that really got 10x faster while sticking with HTML, CSS, and java-script so it's possible. The trick is stick with competent people and reasonable designs.
I believe it's been discussed many times before. Developers who use jQuery do so because it provides a good API / abstraction layer, as dealing with browser specific issues could be non-trivial.
Sure, it's 'worth it' because nobody cares if a web app takes 1/2 second to render, but as soon as you trade speed for anything else you quickly end up with code that's as slow as your willing to live with.
Having said that there are a few modern web-apps that really got 10x faster while sticking with HTML, CSS, and java-script so it's possible. The trick is stick with competent people and reasonable designs.