This API exposes the so called driven properties, which are aimed to map any type of node properties (i.e. title, body, taxonomy, CCK fields, workflow, etc).
What such driven properties are used for depends on the modules taking advantage of them.
The only module with UI (i.e. measurable by end users) distributed within this project is "Driven Node Edition Policy" which allows to selectively hide properties from node edition on per-property case basis and if "Driven Access Control Policies" is also enabled then it will take advantage of it and allow per-roles configurations.
But the principal module relying on this API (from which this project got split in fact) would be Comment Driven.
Nevertheless, other modules might find helpful to have an API like this, and feature requests will be welcomed.