It's not a commercial application, but I have 2 raspberry pis rack-mounted[i] running some utilities for my home network (pi hole, gps-based NTP, ads-b data for FlightAware). Using PoE means no USB power bricks, no USB cables running all over the rack, and one less thing I need to plug into my UPS.
[i] https://www.amazon.com/dp/B08F9X528J