By generating an audio version of Canvas content, it becomes possible to read the original content in an mp3 file. In addition to people with visual impairments, an audio version also helps:

People who prefer listening over reading or are more auditory learners
People who want to read and listen to the content simultaneously
People who experience reading fatigue when dealing with large documents
People who want to multitask while studying, such as commuters

The first time you generate an audio version of a file, it may take from a few seconds to a few minutes to generate. There is a limitation for larger documents of 100,000 characters, approximately 30 pages of content.