User interface components, such as links, buttons, and input fields, often have two types of labels: a visible label and a programmatic one. Did we just blow your minds?
Speech input and text-to-speech users would have an especially hard time if the visible labels on your site don't match the programmatic ones. Speech input software recognizes the programmatic labels for user interface components. However, if such a user is trying to, say, navigate a website by its side menu, they would speak the visible label of a link in order to select it.
If the programmatic label doesn't match the label the user sees on the screen, the speech input software they're using won't recognize the command.
Similarly, text-to-speech software reads the programmatic labels featured on a page. If the labels the software reads don't match what the user is seeing on their screen, it could lead to a fair amount of confusion.