Always. My players don't know their characters' hit points, so all the numbers are kept behind the screen and they get a narrative representation of what's going on.
Bizarre. OR... awesome!See now, this is bizarre to me. I like to have my players know what's going on mechanically. This is partly because we're all aware it's mechanical abstractions and we're cool with that, and partly because I really don't want to keep track of everything myself.