Once we articulate the business process in a separate layer of the SOA, the potential business benefits include crisis management and business continuity.
A business may need to roll out an amended process very quickly, to deal with some crisis. Subject to appropriate controls, we can envisage a company defining and testing a small change to the BPEL script, and then making the new service available for use around the enterprise. The elapsed time from detecting the problem to operating the amended BPEL script might be measured in hours. (Please let me know of any actual benchmarks.)
Of course, an urgent crisis might call for an even faster response than this. There may be a sudden change in the environment, making the current way of doing business uneconomic. There may be a serious security breach. The company is haemorrhaging value, but the prospect of totally shutting down the business process until the problem is fixed is not an appealing one. With BPEL, the process manager should be able to switch over to a previously defined (and thoroughly tested) safe version of the business process (with reduced functionality, increased security, perhaps increased manual intervention, and hopefully reduced vulnerability) to maintain some form of business continuity, in the same manner as reverting to an alternative service.
There is a general point here that we have made before in other contexts. If you want to be confident of flexibility, you need to regularly exercise that flexibility. Don’t wait until you have a crisis before you discover whether your process management is flexible enough. Run the safe version of the process for (say) an hour every month, to make sure it still works.