In my area of software, we provide customised solutions to large enterprises. We have an app that takes in a lot of dimensions about each issue report and spits out an "objective" severity. This app has been honed over 20 years of reviewing issues. That's the only severity that's allowed into JIRA. By default, the priority is set the same as the severity. When we review the issue list with the customers, however, they are free to adjust the priority according to their unique business needs, and developers work on issues in priority order only, not severity. It's a good system, and it ensures that we're working on what the customer needs and not our isolated view of severity. Granted, we will consult with the customer during triage and give them a steer based upon our experience, but they have the final say.