When writing TestStand UI components using LabVIEW, there are a lot of scenarios where using a callback VI to handle a TestStand event is the right move. As of writing this, that's the only way.
There have also been plenty of times when I would have preferred to handle a TestStand event directly within a LabVIEW event structure. In these kinds of scenarios my code would be less complicated if we had the ability to directly register TestStand engine events with LabVIEW's "Register for Events" node.
Years ago when learning TestStand, I tried to do this out of intuition and I was kind of surprised that it wasn't supported.