It is used for a serialization to a file. An example of a regions file defining two polygons is here:

https://github.com/nden/code-experiments/blob/master/generalized_wcs_api/prototype/polygon_region_example.json

The schema follows the definition of regions in the STC document which really defines their format. It is simply the implementation of this format in JSON. I could have used XML or ds9 definitions but for various reasons I chose JSON. It doesn't really matter. As I said in the beginning of `wcs_api` this data model has a second part to it which I am not addressing here, namely its serialization to a file. JSON seems as a plausible choice as anything else but I don't want to divert the discussion to serialization because it's really a separate issue.

Regions are used in many contexts and I think eventually we probably would have to support multiple serializations including `ds9` regions.