Persistent Chat Server is a new functionality of Lync 2013 (Lync Server 2010 had the group chat that was really different). Persistent Chat enables chat and IM conversations to be continued over time. Some of the more interesting new features related to Persistent Chat in Lync 2013 are the administrative interfaces integrated in the Lync Server Control Panel, the deployment managed through the Topology Builder, and the new solutions dedicated to high availability. Persistent Chat is a Lync role that can live by itself as a single server or as a dedicated pool, but the Persistent Chat Front End could also be collocated with a Lync Server 2013 Standard Edition.
The main advantage of the Persistent Chat Server over a normal mail communication is that the entire flow of conversation is always available. People who will take part in the conversation a second time have the opportunity to read all the information that has been exchanged. Persistent Chat is also powerful as a single reference point, where all the users interested in a certain project are sure to find the data they need. Scenarios such as brainstorming and sharing information between employees at different workplaces and working shifts are the best ones for such a feature.