Uses of the Image API
The Image URL can be used in the same way as a normal image and has lots of practical uses.
Embedding on web pages:

A home teaching background for a menu:

Zoom Viewer:
The most common use case is to show the image in a viewer like OpenSeaDragon:
National Museum of Sweden
Some places embed a IIIF Image into their content management system and it means they don't need to use the Presentation API. For example: