“Without a style guide, high-fidelity mockups are the best way to communicate a new feature to developers. Unfortunately, though, pixel-perfect mockups almost always result in duplicative and wrongly abstracted code. Why? First, fidelity alone (without good annotations) does not communicate the abstractions you intend. Without knowing how the designers conceive of the design language, developers may make different modeling choices and make the code difficult to maintain. Second, higher fidelity can unintentionally signal novelty. Developers may think that you mocked up something in higher fidelity because it is a new UI component, and thus fail to reuse existing code. This slows down development and results in bloated, less maintainable code.”

(Jim Lindstrom a.k.a. @jimlindstrom ~ UX magazine)