From Monotype's blog:
The job of typography is to deliver legible, accessible, attractive content regardless of the medium. Type is language. It’s the foundation of branding and brand expression. The right type reinforces a great message both by carrying a literal meaning and conveying emotion and personality. This is especially true in today’s mobile device environment, where web design often must be pared to its simplest form.
Thankfully, the tools available for working with type on the web have improved dramatically. Until recently, live web type was only viewable at the end of the design process, when a developer began an HTML prototype. Web designers were stuck using system fonts or images of web fonts to approximate the web typography they hoped would materialize at the end of the project—only to watch those designs unravel during the development process.
With today’s typography design tools and the availability of web fonts through online services such as Fonts.com, MyFonts and Google Web Fonts, designers can create web typography earlier, faster and better than ever before. Moreover, they’re no longer tied to a small handful of system fonts and are free to experiment with classic and contemporary typefaces.
By seeing type first—in the browser at the start of the design process—designers can review the entire composition using real content rather than evaluating specific characters. In real-time they can see how fonts render across browsers and different devices before the prototype is built and before committing to final type decisions.
That’s where the beauty and flexibility of responsive design is transforming the entire web design process. And this is the perfect time to put things right by placing type first.