A Parallax Website depends heavily on a scrolling effect on the main page. It does contain a navigation bar but when you click on menu options, it scrolls down and lands on respective section on the same page. So, a visitor can view all the fields just by scrolling down on single page which is mostly the homepage.
Basically , layering up multiple backgrounds and objects (such as images) and then allowing them to move at different speeds creates a sensation of depth and dimension. Making the entire website quite attractive in terms of look and feel.
Parallax Design per se is pretty good for visual impact. However, it makes a bad choice in website design when designers choose to show all pages of a website within a single page scroll. While the site visitor is tricked by Parallax Design effect into believing that multiple pages are being visited on each click, it is actually one single page that loads in actuality, mimicking visits to multiple pages.
For example, in most One Page Parallax Design websites, when visitor clicks on ‘Services’ in the main navigation for example, instead of being taken to “domain.com/services” (i.e. a different page), the URL changes to domain.com#services and you will be automatically scrolled down to the ‘Services’ section on the same page. Here the downside is that search engines would index the only a homepage but not the complete URLs, (the hashes in the URL that act as a shortcut (anchor-tag) to another part of the same page). So, a parallax website is not always search engine friendly.