People with disabilities face many accessibility barriers when they try to access websites. One common barrier is a lack of meaningful text descriptions for graphical elements on a website, which affects individuals with visual impairments who use screen readers. Another common issue is related to the use of keyboard versus mouse controls. If website content is only available via the computer mouse, people with physical disabilities may not be able to access it. In addition, complex web pages that contain many elements such as animation, video, and audio and that have confusing or inconsistent layouts can be difficult for people with disabilities to access.
Some website developers, in an effort to make their websites accessible, provide two versions of their website—the "regular" or primary version and a text-only version, which contains the text of the website without any associated graphics or media files. However, there are serious drawbacks to this approach. Because additional text-only websites can be expensive and difficult to maintain, visitors are concerned that the text-only site may not be updated as regularly as the primary site. Often, text-only sites are also not fully accessible.
Many web developers believe that a text-only version of a website completely addresses issues of accessibility. In fact, while text-only sites are usually accessible to a person using a screen reader, users with partial sight, learning or cognitive disabilities, limited hand use, or hearing impairments may find the text-only site as difficult or even more difficult to access than the regular site. These users are better served by a web page that is consistently organized and laid out and that allows them to resize the text and graphics, access audio content in multiple ways, and navigate the site by using the keyboard alone. It is worth noting that people with and without disabilities may have bandwidth limitations or old hardware and software and may have difficulty accessing complex websites. Accessible web design improves access for these people as well.
Another problem with text-only sites is that they create a situation where an organization has to maintain and update two parallel websites. Often, due to time and financial constraints, the text-only page is not kept up to date. With an outdated text-only page, the current content of the primary page is still inaccessible. At this time, there is software available that can create and/or update text-only pages automatically, but the updated pages still need to be checked for clarity, and many users distrust that this check has been done. The web standards community is currently working toward creating a World Wide Web where content will be entirely separate from presentation and will be delivered to users in the form that makes most sense for the individual user and the user's technology (e. g., screen reader, web browser, wireless phone, handheld computer). In fact, there are many database-driven websites on which text and graphic versions are automatically generated on the fly. However, until this practice becomes widespread, the problems with text-only pages will continue to keep many blind users (the primary target of text-only pages) from using them.
The World Wide Web Consortium's Web Content Accessibility Guidelines 1.0  state that text-only pages should only be used as a last resort:
11.4 If, after best efforts, you cannot create an accessible page, provide a link to an alternative page that uses W3C® technologies, is accessible, has equivalent information (or functionality), and is updated as often as the inaccessible (original) page.
The Section 508 Standards  make a similar statement:
(k) A text-only page, with equivalent information or functionality, shall be provided to make a web site comply with the provisions of this part, when compliance cannot be accomplished in any other way. The content of the text-only page shall be updated whenever the primary page changes. (Emphasis added.)
Overall, it is much more effective, easier, and less expensive to design and create one accessible website from the beginning than to create and maintain parallel sites. The Section 508 Standards and the Web Content Accessibility Guidelines are excellent resources for learning to design accessible websites.
-  Web Content Accessibility Guidelines 1.0
-  Section 508 Standards