When a new user arrives at your website, they will be faced with a new environment that they are not familiar with. It is therefore imperative that web design incorporates logical navigation.

The standard practice of having some kind of navigation at the top of your web site works well because this is the first place that a user will look. If they don’t find anything at the top of the page, they will look down the left side; then the right side and then they will probably stop looking.

If your web design brief is to create a a site that people will stay on, then the web site navigation should be large and prominent. Most news websites and corporate services websites will incorporate this principal.

However, if your brief is to create a web design that makes fast sales, then you don’t necessarily want to encourage people to bounce around the different pages on your website and gradually lose their impulse to buy or interact. In these kinds of web sites, navigation should take a back seat to the main sales copy. Many web sites will have lost the sale as soon as the user navigates away from the page they entered into, so the objective is to make the navigation area visible but not prominent.

Dropbox is a perfect of sample of how single objective web design can incorporate logical navigation. Most of the real estate on the home page is taken up by the explanation video and the download button, but if you look down the bottom of the homepage there is logical navigation.

Web design is about providing everything to everyone, but controlling how everything is delivered. You need to give users a way to move around your site, but if you would prefer it if they stayed put, then make your copy more interesting than the navigation menu.

Source -
http://en.wikipedia.org/wiki/Web_navigation
http://www.resultfirst.com/design-and-development/