Accessibility Labels provide metadata about your app, so that for example screen readers can access the elements in your app. They are critical for blind users, user with low vision, users with mobility disabilities and users with memory loss. Missing labels will make your app inaccessible for many users.

For some organizations, providing accessibility labels is mandatory, by law or by policy. In any case they are a good idea.

Apple has a video, Writing Great Accessibility Labels, which explains more.

An accessibility hint is additional information a user may need to interact with an element. You can think of it as instruction on how to use a control or button. This is particularly important for blind users, user with low vision, users with mobility disabilities and users with memory loss. Missing hints will make your app inaccessible for many users.

For some organizations, providing accessibility labels is mandatory, by law or by policy. In any case they are a good idea.

For example, you have an "Add" button that adds an item to a shopping basket. A good accessibility hint in this case would be Adds the item to the basket. The label "Add" does not say what is added to where, and therefore we need an accessibility hint with the additional information.