The Work Items - List API uses Get method with the optional parameters (ids, asOf, fields, etc.) added in the URI, which can be limited by the URI length.

While Work Items - Get Work Items Batch API uses Post method with the parameters in the request body, allowing for larger payloads.

Therefore, they can both work when the request to call is relatively small. We can use the POST request when attempting to retrieve a large number of specific work items with parameters.

See the discussions on Can HTTP POST be limitless? and What is the maximum length of a URL in different browsers?.