The problem I've found is that most people in my area use narrow gauge (stainless?) nails on fascia, which do a poor job of holding over time. In my first house, I had a section begin to sag away from the boards over the garage. I noted rain was getting in and later, when my father-in-law and I pulled it back from the boards, we discovered the board had completely rotted out in places. After pulling maybe half the sheets off, we found the nails were sagging all around the house (in addition to some of the boards not being nailed flush to the tails of the rafters). Cost us some $50 in lumber and a good day of replacing bad or poorly attached boards.
When I put the fascia back up, I used #8 2" pan head stainless steel screws (the pan head is more important than the length, as I've used 1" without issue). Pre-drilled holes where the nails had been and the screws went in easily (don't cheat and try to power them in or you'll strip those softer screws out). The pan heads cover the holes pretty well, they suck-up to the wood, and they don't work their way out. Period. Those screws are probably still up there, along with all that wood we replaced.
The caveat here is that my fascia had a "drain gutter" so that water that did hit the substrate would roll down into there and fall out in the piece breaks. I would be less inclined to do this on fascia that doesn't allow the water to drain away from the boards. It's unclear if your fascia does that.