In composer (and in photo center on galleries), media items can have certain field values overwritten when included on a piece of content. This is a great tool in the ability to tell meaningful stories. In the API, that custom value completely replaces the original version of that field.
Instead, it would be incredibly helpful if the original values were included somewhere (maybe additional_properties?) regardless of if a custom value has been set.
For headless clients, the ability to persist data in cache and local data stores greatly increases speed and reduces the risk of hitting API limits. Without the ability to tell if a media item's metadata has been overridden, it makes it very difficult to persist those items.
For example, If we were to persist an image from an article that had a custom caption, we would potentially be delivering the wrong caption if the image data was served from the data store. Instead, if the API results contained both the original and custom values, we could ensure that no custom values were sent to the wrong place.
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