See this feedback from 360Giving pasted from this thread:
The ability to include third party identifiers for locations significantly increases the user-friendliness of sharing geographic data, as latitude and longitude are not always commonly used to describe service delivery locations.
However, we would recommend against highlighting what3words as an example of an external identifier scheme, as it is fraught with issues, and this may increase its perceived legitimacy.
It is not clear whether there are any limitations on the types of third party schemes that can be used for sharing location data. 360Giving has had some experience with this, and found that as a result of our geocode types list not being validated, it has suffered from poor data quality and a proliferation of codes which is now unwieldy, while the official codelist has become out of date. We would recommend defining a closed list of schemes and maintaining that list to reflect changing needs, rather than being permissive of any scheme being used, which makes the data harder to map and compare.
We would strongly recommend supporting the use of externally referenced geocodes for all entities that relate to location, for example service area. This would make the data more comparable to other datasets, including being able to compare the provision of services to the area of impact of grants, or to government administration and reference data. Consider introducing a concept of location scope or similar for indicating a reach of a wider area than a single place.