There are a number of ways in which consistency contributes to the success or failure of a site. Primary considerations here should be avoiding user confusion, adhering to Web design and presentation standards, and ensuring that the Web site is perceived as being well planned and professionally executed.

For commercial sites, you will want to achieve a consistent look and feel throughout the site. Companies with a strong brand identity will probably want the branding to be present to some extent on every page.
This does not mean that every page has to look the same. Different sections or sub-sections of a site may have differing formats, but with careful planning and design, you can preserve the customer's sense of orientation. Design choices play a big part in keeping the customer aware of which site they are at, and which part of the site they are visiting. If a user feels they are "deep" within a site, or that there is much more useful material that they can explore with ease, they may be less likely to leave.
There are many strategies for achieving consistency, such as:

Imagine if you visited the Coca-Cola site and the colors were not red and white, and the well-known swooping, white, script font of their company brand was nowhere to be seen. You would probably wonder if you were actually at the official Coca-Cola Web site. Web sites can enhance brand identity, and should certainly draw on existing brand familiarity.

On a commercial Web site, signs and metaphors should be interpreted by a variety of people in a consistent manner. In designing for a wide audience, there is often a thin line between being creative and causing user confusion. For example, you might think that e-commerce site designers are not being creative because the majority of sites use a shopping-cart metaphor to make purchases. Yet this image has become easily recognizable on the Web, which ensures almost universally consistent interpretation.

If the majority of your audience does not interpret your signs and metaphors in a consistent fashion, the site may actually detract from your business objectives. Rather than developing a stronger relationship between the site and its customers, a site with inconsistent signs and metaphors will distance customers from the company, decrease the chances they will return to the site, and lower their opinions of the company in general. The best way to ensure consistent interpretation is to validate signs and metaphors by testing them on target audience members.
Question: What are some strategies for achieving consistency of signs and metaphors on a company Web site?
Answer: Use of a company logo on every page; use of branded colors, images, or typeface; navigation that ties in to branding.

In the next lesson, you will study how the layer of signs and metaphors work together with the layer of information architecture to build success for your site.