@Niall, when you say “easier” do you just mean that there is a specific field to match against rather than using process variables?
From what i can tell from the API Docs, whenever there are times where you would use the business key as a filter/search criteria (example: finding all process instances with the specific business key), you can also use the process variables.
Is there any benefits of the business key over process variables, where the “feature” or “benefit” does not have a process variable equivalent?
The biggest barrier we find to using the business key is its inability to set the business key after the process has started. Can a business key be set as part of a start event execution listener?