I agree with your sentiment @dennish. I definitely didn't think it was relevant until I got the model on the test layout.
Here are a few hints before painting that will help you out...
If there are an nails coming down from above, take a dremel and cut them flush with the subfloor. It will look better and helps with drips while painting.
While primer is not necessary, if you have sheet metal ducts that will be painted, you might consider priming them as the paint will stick better. Without primer the paint will easily scratch off the duct work.
Other than that just make sure to vacuum the ceiling a bunch of times to clean out the dust. I also recommend using a compressor and blowing the remaining dust out. Nothing worse than when dust and paint meet!