Why fentanyl would be prescribed for less than excruciating pain?

Level 10 pain. Not relieved with oral combinations and long acting opioids is the usual reason for the patch, but adverse affects with the other products (obstipation/consitpation, nausea and vomiting at even low dose) could be a reason. The golden rule is to use as low dose and start with uncontrolled and go up until pain is conrolled. Fentanyl is also expensive.