Android Programming: The Big Nerd Ranch Guide, 4th Edition

Creating a Comparable Experience

You should specify a content description for any UI widget that provides information to the user but does not use text to do it (such as an image). If there is a widget that does not provide any value other than decoration, you should explicitly tell TalkBack to ignore it by setting its content description to null.

You might think, “If a user cannot see, why do they need to know whether there is an image?” But you should not make assumptions about your users. More importantly, you should make sure a user with a visual impairment gets the same amount of information and functionality as a user without one. The overall experience and flow may be different, but all users should be able to get the same functionality ...