Why does DynamoDB have a "DescribeEndpoints" request?

One of the API requests that DynamoDB has is DescribeEndpoints. According to its documentation, it "Returns the regional endpoint information." Basically it returns something like dynamodb.us-east-1.amazonaws.com when connected to us-east-1. But, how is this useful? If I'm already connecting to the us-east-1 endpoint to make that request, it means I already know the endpoint address, don't I?

But I'm worried that this request is actually worse than just useless. The thing is, it only returns an address, not a full URL - the endpoint returned does not list a scheme (http or https) or port number. So if a program wants to use the result as an endpoint, it needs to guess the URL scheme and port (e.g., https and 443). This guess would be wrong on, for example, DynamoDB Local or ScyllaDB Alternator - for example the former runs by default on http port 8000. I noticed that, perhaps for this reason, DynamoDB Local does not implement the DescribeEndpoints request at all.

So my question is: Why does the DescribeEndpoints request exist in DynamoDB at all, and under which circumstances should a DynamoDB application use it? Also, is it fine that DynamoDB Local decided not to implement this request at all? What sort of application might break by the missing DescribeEndpoints support?

What led me to this question was seeing what the new DynamoDB Shell (which is written using the AWS C++ SDK) does when given an endpoint URL (e.g., DDBSH_ENDPOINT_OVERRIDE=http://localhost:8000/). The first thing it does is to call DescribeEndpoints and then use its result to replace the endpoint URL, in a broken way - it takes the new address it gets in the response, together with the port number "8000" from the variable but incorrectly sets the scheme to "https", and unsurprisingly the result mix doesn't have to work... It does work on DynamoDB (without the endpoint override) and DynamoDB Local (which doesn't implement DescribeEndpoints) but fails on ScyllaDB Alternator.

In DynamoDB you don't need to specify an endpoint as it's implicitly decided based on the region set for you client.

I've found DescribeEndpoints valuable when troubleshooting issues such as ResourceNotFoundException which was able to highlight that I was not connecting to the region I believed as the region was being reset outside of the config class.

As the endpoints for AWS are "implementation" detail then they can be subject to change, in which the DescribeEndpoints API would be beneficial in that case. As DynamoDB is 12 years old it's highly likely this API was created before the endpoints followed a rigid schema.