The following is a guest post by Jack Doyle, author of the GreenSock Animation Platform (GSAP). Jack does a lot of work with animations in the browser and has discovered that the generic opinion that "CSS is faster" just isn't true. It's more than that, as well. I'll let him explain.
Once upon a time, most developers used jQuery to animate things in the browser. Fade this, expand that; simple stuff. As interactive projects got more aggressive and mobile devices burst onto the scene, performance became increasingly important. Flash faded away and talented animators pressed HTML5 to do things it had never done before. They needed better tools for complex sequencing and top-notch performance. jQuery simply wasn't designed for that. Browsers matured and started offering solutions.
... read the whole story at css-tricks.com.