The choice component allows you to semantically group multiple components, but only allows one of those components to be used at a time. This enables polymorphic components when editing the content.
With the choice component, you can define shapes that allow editorial users to, for instance, manage different types of hero media like an image, video, or relation to a richer media item. This still maintains semantic integrity with all choices being grouped as hero, but the editorial user can only select one when creating the item.
To use another example: there are different sets of properties that describe a TV vs. a refrigerator. The editorial user can click on the appropriate set of properties to define during product creation.