Having knowledge of both design and development is invaluable. It gives you insight to what's possible to implement when designing and can help you develop a roadmap of how to hand things off to developers. Aside from making you a lot more desirable to employers, it helps when designing to imagine the code in your head which could increase development speed and improve your knowledge of coding as you design.
Perhaps I'm bias because I do the things mentioned above. I'd be interested to see a reply against this.
As a designer/developer:
Having knowledge of both design and development is invaluable. It gives you insight to what's possible to implement when designing and can help you develop a roadmap of how to hand things off to developers. Aside from making you a lot more desirable to employers, it helps when designing to imagine the code in your head which could increase development speed and improve your knowledge of coding as you design.
Perhaps I'm bias because I do the things mentioned above. I'd be interested to see a reply against this.