Earlier quoted context omitted.
Sure, if you don't know Photoshop very well then you could code it faster. Except you will end up with sloppier code and a weaker design. It is the equivalent of building a house without blueprints. You can do it, but if you take the time to plan things out before you break ground you will end up with a stronger product. Now, if you already have a design style locked down and code you can just puzzle together then su…
I understand your general gist... but I find sketching the design by pencil and paper much faster than photoshop - obviously I don't get pixel perfect results, but the intricacies of CSS mean that it's difficult to match a photoshop design pixel-by-pixel anyway. I agree that it's much better to have a visual plan in place first, but photoshop would definitely slow me down, and I've designed dozens of web sites.
Sketching doesn't give you a realistic sense of space and feel for web design. Very often you can sketch something that looks good on paper, but once you put it on the screen it just doesn't translate well to a pixel medium.
Sketching is great if you are working with a physical medium like brochures or posters though. Then it doesn't suffer from the same translation cost.