Okay, so many if not most RPGs represent an entity's ability to sustain damage with point values. These points are often called "Hit Points" (HP) but may go by terms such as Health Points, Structural Damage Capacity, etc. They can be used for living creatures or objects. Having more points means that the entity can sustain more damage and vice versa. This is a straightforward mechanic and one easy to understand during play and implement in design. For a given game, the relative value of an individual hit point can vary, in the sense that some games allow maximum HP values into the hundreds (even up into the millions for later bosses in World of Warcraft) while others max out at five or ten. I refer to these relative values as "big HP" (where there are few per entity) or "small HP" (where there are many per entity).
Using hit points allows for more granularity in damage, including very minor damage. A two-handed axe doing 1d12 damage may only do 1 HP. Systems which have just a couple injury levels and a "toughness save" to avoid taking injury lack this granularity. I find the granularity of HP weapon damage extremely handy as a GM because I can fudge weapon damage behind the screen if a scene calls for it.
Most of my gaming in recent years has been D&D 3.5 and Pathfinder, both of which are classic HP-based games. I'm generally fine with the concept of hit points. But more recently I've decided that I'm not happy with the power curve that increasing HP introduces in D&D/Pathfinder. At upper levels, PCs and NPCs are so powerful as to be superhuman. Even by middling levels the characters are almost immune to most normal individual threats, such as taking a heavy crossbow bolt to the head. This means that you either have to up the ante outrageously, such as threatening them with a gigantic lightning bolt to the head, or rely on them being good roleplayers.
The problem here is that I want to run a swords-and-sorcery fantasy game, not a superheroes game. I do want the PCs to advance over time, but not to such a great extent. I prefer a style of game which floats in between gritty-tough and high fantasy. So either I have to quit playing D&D/Pathfinder or find some easy way to crank down the HP given and taken. Or I have to find an existing system and graft on the bits of Pathfinder which I really like, which is mostly the wide array of classes. As I've mentioned in earlier posts my imagination was captured not long ago by Old School Hack (OSH). OSH uses hit points, but they are "big" hit points, in that PCs start with 5 and even big monsters don't go much past 25 at most. OSH also ties its hit points ("wounds") in with damage effect levels, such that light injuries have no effects and heal quickly but serious injuries have effects are take longer to heal.
I really like having increasing HP loss lead to the victim entering various stages of wound effects, such as by using a wound track. A wound levels system provides several benefits. It avoids the problem with hit point systems, particularly in the high-volume "small HP" systems, where you're at 100% efficiency until you lose that last HP and keel over. It allows players to refer to their current health status with a descriptive term, such as "Friend priest, I am gravely wounded" rather than crappy game terms "Hey you with the cleric, I'm down to 4 out of 15 hit points here".
Another thing which a combination HP/injury level system provides is application of some penalties as the injures become serious. However, if the penalties are too severe then you get a "death spiral" effect where the more wounded one is the less likely one can successfully take any actions. In a very gritty modern game this is actually a great mechanic, but it's not what I'm looking to apply to my fantasy RPG campaign.
My motivation for taking time to look at hit points is to help work out what set of rules I will ultimately settle on for fantasy role play gaming. My gut reaction is to go with Pathfinder. I have a basic attraction to rules-heavy systems (what I call "complete" rules systems) and it has masses of published support material ready grab off the shelf. On the other hand it has the "superhero" problem at high levels and the sheer mass of material is a bit overwhelming. I think I will be sticking with a hit points based approach, but am still weighing the pros and cons.