In article .com,
says...
Gurus:

I had a new roof installed after tearing off the old one. The nail
points are protruding (nearly 1/4") through the underside of the deck,
in the attic. That could be a safety issue in areas that we use for
storage. I sure wouldn't want to come up between the rafters and slice
open my head on a sharp nail!

Wear a hard hat.