Identity, called "branding" by the advertising industry, is the cornerstone of every well-designed Web site, because your Web represents you or your business globally and continually. For that reason, identity should encompass every aspect of design, from a site's overall structure to its graphical look and feel to the choice of fonts and column layout.
Significantly, identity shouldn't stop at the welcome mat. Every page at every level should contain some similar style as well as consistent navigation techniques.
The goal of design is to create an experience for every visitor that provides a quickly understood, intuitive metaphor for a successful interactive relationship. That is critical for not only complex database-driven sites, such as catalogs or knowledge bases, but for small sites as well.
One of the most important design considerations is making sure that users can quickly get their bearings anywhere in the site by making the organization as intuitive and seamless as possible. Users should not only know instantly--and if possible, instinctively--whose Web site or intranet they're visiting but also where they are within the overall site structure. Naturally, the optimal time to create this effect is during the site's initial planning stages, as choices made then set the stage for--and greatly simplify--all decisions that follow.
( See more at Elements of Style.)