Except that native forms are clunky and the validation is very basic. Javascript can save you some unnecessary requests to the server with quick & easy initial

Except that native forms are clunky and the validation is very basic. Javascript can save you some unnecessary requests to the server with quick & easy initial validation checks & allow you more control over the behavior of the page after form data submission (via xhr). Javascript is also currently faster for animating, and can do a wider variety of animation.