Design is a process. At every step in the process, you're constantly re-doing the same thing, trying to figure out what's actually write.
Product design greatly improves when you get to code faster. Er, why?
It elevates the conversation. Real data! Real feels! Real interactions! With prototypes, you can actual test it.
It protomotes systemic design. Design components across pages, not pages of components.
It allows us to speak the same language. Coded components instead of pixels and design specs allow us to work together.
This refers to the mobile clients that came out three years and a day ago on twitter.com.
They did a bajillion Photoshop mockups. Whenever you had to update one, you had to update ALL OF THEM. Terrible.
Then, they prototyped. EXCEPT THEY WEREN'T BECAUSE NO TIME FOR PRODUCTION-WORTHY CODE.
Consolidate similar design components into one. Getting into code faster allows you to find these things faster. Instead of having six slightly different things, just have one. Less time!
Speed is a feature. Having those components made them move faster so that they could worry about speed, because on a site like Twitter, speed is hella important.
If you have something prototyped, you can get it approved.
It's not that old design techniques are antiquated and you should code in the browser and blah blah blah. Because sketching is awesome. It's just that you should try to move into code faster to get things shipped faster.