First and foremost, web accessibility makes web-based information and services accessible to people with disabilities.
Adherence to the Section 508 Standards also allows institutions to be in compliance with U.S. federal law.
There are many additional benefits for organizations and individuals without disabilities. Captioning assists those for whom English is a second language and improves retention for all audiences. Web accessibility standards benefit individuals with age-related impairments, people with temporary disabilities due to injury or illness, and those with learning disabilities. Proper coding makes your website more searchable and thus increases search engine optimization for both site and content; it also improves web page download times and reduces server load. Websites are easier to manage and update. Interoperability improves between browsers, operating systems and mobile devices.
Simply put, web accessibility is good practice.