There are definately a large variety of use cases being kicked around that you wouldn't always think people would want or expect.
* Federated Searching: "Actor/User Agent needs to seamlessly query/access/integrate related chunks/pieces of data coming from a set of decentralized heterogeneous sources, and get presented an unified view over a the whole result-set/data-set."
* Temporal querying.
* Regular Expressions.
* Discover functionality of server: "Abelard's client software connects to each RDF storage server and determines whether it supports one of the three query languages it knows about. Abelard's client software chooses, based on priorities set by Abelard, to send different queries to different servers."
They seem to be missing security - probably required in the federated searching use case.