Designers should move as fast as possible to the browser. What you see is what you get. No more spending time measuring every pixel before handing it over to engineers. It’s all in the code. You can easily iterate on your design without having an engineer to help you. Less questions and meetings with stakeholders, clients, engineers = Time saved = Money saved. Animation is no longer an afterthought. You actually think more about how a hover state should animate, or how you can solve the problems better with interaction. Sketch is great for getting a general concept of what you want to build together. But move to the browser as fast as you can. The benefits listed above should answer as to why.