Services are bots, programmable contexts that have largely been replaced by rooms in PSYC. They differ from rooms in that their interfaces are more like persons, which in most cases would complicate the user experience. While IRC-like services for room management may not be necessary in PSYC, there are other applications that may require or benefit from services.

Onion Routing

Onion Routing is a technique for anonymous communication. The destination context can rely on the signature of the innermost message layer to authenticate the origin of the message without needing to trust the delivery network.

This technique is best implemented as a unicast context.

Natural Language Interfaces

If the user interface for a program were to use natural language rather than a command language then it may be beneficial to use a unicast messaging metaphor to interact with the program rather than doing so in a multicast context.

More

Maybe. :-)