Every web site has an optimal design that fits perfectly with your theme, requirements, and type of visitor. For example, a web site that offers electronic postcards need to attract the attention of the visitor’s eyes, using images, animations and interactivity, while a site devoted to science, teaching or research may not need any of them to show your information and content. The amount of animation and interactivity without doubt affect the accessibility of your web page, given that the technologies used to provide such content are usually not supported by user agents or often not designed for people with disabilities. To consider how many people you could be leaving behind, I rely my study in statistics of this site (HTMLQuick.com) which is fully accessible and provides a large amount of textual information. To see some round numbers would say that if the content of the site is completely based on Flash or JavScript We would be losing from 1.77% to 4.55% of visits only due to the lack of technology, which could be a large number of visitors if it’s a successful site.
But let’s look at some considerations based on the most popular and problematic technologies available. Flash Flash is an excellent way to build animations and interactivity, but can also be a big problem of accessibility. Create a website completely in Flash could leave out a 2.78% of the visitors and make a completely empty site for search engines, which can represent your first problem. Many sites will see Flash as a first necessity while others will only used for animations or simply not used. If your site does not need it, then try to use it only for animations or by providing rich alternative texts. Avoid build Flash menus, a user agent that does not support it may not follow its links. Exports the swf file using the lowest possible version.