Depending on the objectives of the anlysis you can create rules on top of the information that the engine is externalyzing based on the process execution. Or you can consume the information externalized by the process engine as events that can be analyzed by Drools Fusion, that will allow you to react in real time to the situations described by your rules.
First up - this question is more about the enterprise-wide thing around BPM as opposed to jBPM and I'm going to answer it from that perspective.
Standards-based BPM (business process management) is an opportunity for enterprise value. We (users of BPM technologies) have the opportunity to move away from enterprise-centric encapsulation of business logic towards a world where business logic is centralised but more importantly - dissociated from applications.
Instead of writing the business logic in Java or PL/SQL or the special language/API bundled with your favourite application, you have the opportunity to position that application as just an implementation of an information service. You use business processes definitions to define how that service is used, and you do it with standards-based definitions. That means freedom, freedom from proprietary solutions means saving, big saving.
Big savings - they tend to have an impact.