I've been thinking about damage in RPGs, and the different roles it can play. Here's the ones that have occurred to me:
1. DAMAGE MAKES YOU LESS EFFECTIVE: for instance, Burning Wheel, and any other game that applies penalties as you start taking damage. It's a death-spiral, since it makes it harder to not get more injured, but sometimes that's what you want for genre reasons and/or gameplay dynamics (e.g. BW or The Rustbelt). Interestingly, BW does this without doing no. 3 below -- taking more hits doesn't really get you closer to suffering a mortal wound.
2. DAMAGE MAKES YOU MORE EFFECTIVE: like most action movies -- as the protagonist gets beat up, he gets more and more dangerous. Blood Red Sands allows you to do this, although it's not a given, since damage can take the form of traits. Sorcerer does it in conjunction with no. 1 -- using the "Will trick" to overcome incapacitating damage, you can actually end up with more dice to roll than you would have if you were fine.
3. DAMAGE EDGES YOU TOWARDS THE POINT WHERE THE FICTION DEMANDS YOUR DEATH: hit points do this, especially if you apply the loss of hit points as something other than actual wounds and blood loss, like many OSR folks: HP loss means getting tired and sore, up until you lose those last few, and that's when it means getting a sword through your gut. The other prong ("Blood") of Rustbelt's two-pronged damage system also does this.
4. DAMAGE PROMPTS EVENTS OR CHOICES: Poison'd: when you suffer a deadly wound, make a bargain for your life or die. DitV: the Fallout and healing rules. 3:16: flashbacks.
Those are all I can think of, from the games I've had exposure to.
What I haven't seen: damage changing your effectiveness, without making it more or less -- that is, changing categories rather than (or perhaps in conjunction with) magnitude. I'm really interested in this idea. Anybody seen it anywhere?