BPMN has few obvious value propositions:
1. Common notations.
2. Depicts sequence of flow in an e2e process.
3. Identifies messages between various.
It is meant for the whole spectrum of business users both very high level and very detail oriented business process modelers. A set of business users can document their processes; starting from a broad set of activities and decision points to a detailed process definition which captures the intricacies of everyday business including specific details of activities, conditions of gateways, default branches, subprocesses, exception handling and so on.
This will ensure that businesses understand themselves and their processes, are able to document those processes in simple notation and identify the participants. This will ensure that the business can be agile when it comes to adopting new requirements both internal to the org as well as external.
Further it facilitates IT to capture correct business requirements - validate those requirements, understand and capture corner cases. The notation being business user friendly still retains its value.
Another advantage is being able to identify coarse business services which can be further mapped to actual IT services or a combination thereof.
To give an analogy it will do the same to business prcoess modeling as what UML did to software engg, WSDL did to service description.
more details at http://www.bpmn.org