Units are mapped out into as many different abilities as the designer can think of or sees fit to include. As each unit is mapped out with an ability, those with the best abilities are given flaws. This may be something as simple as being more expensive to produce, slower, less health points, whatever. So units are mapped out in a fantastic array of different abilities and flaws so no single unit stands out above the rest. A simple example is an archer has a good range and accuracy, however a swordsman can do more damage and has better armor. In a close range battle the swordsman wins every time, yet in a ranged battle the archer has the advantage. Or a more complicated example is rock beats scissors, paper beats rock and scissors beats paper. Which are in essence the rules of the "rock, paper and scissors" game.
Okay. Now that we've got a hold on what the talk is all about, just where did it all start? Well, in essence the method of unit balancing has been around for as long as games have existed. I think that computer game developers have become more aware of it as an issue and using it to their advantage. I think chess is a good example of a game that has been around for centuries using that style of unit balancing. I mean who is to say a rook is better than a bishop is? Even those who argue the Queen is ruler of the board must face the fact that any Pawn may become a Queen and there are more of them. So even a Pawn must be feared. With computer games it's been key features of Real-Time Strategy games as they start to mature. Age of Empires (Microsoft) and Starcraft (Blizzard) have been applauded for their efforts in using this type of variety. However I think this is simply because RTS is so new that we can see how in previous games the balancing was not as well done. Such as in Warcraft (Blizzard) the water elementals stood as the main weapon of destruction in multiplayer games and C&C (WestwoodStudios) is plagued with tank rushes.
In other genres we can see how this idea has been used for much longer. In arcade style games various power-ups are varied as well as starting characters having different "special moves" yet each being about as good as the next. Beat-em-up games such as Mortal Kombat (Midway) and Street Fighter (Capcom) have a large variety of characters to choose from with different special moves. Although they largely inherited it from Role-playing games that let you choose a basic character class before you start. More traditional strategy has a variety of units but takes little effort to balance them out. So why the change in RTS?
Mutliplayer. In a multiplayer environment designers typically make all the games units available to the player. However if one type is better than players will, rightly so, quickly push to build that type of unit and no other. A recipe for success is created and those who do not follow it suffer. Back where the genre started, Dune II (Westwood Studios), there was no multiplayer option. So the player took the time to take advantage of different units as the AI happily threw a random mix of units against them. So few players under such competition saw any reason to specialize in particular units. Also as the units are slowly made available throughout the campaign, in many of the matches you simply do not have the better units available and are forced to make your way with what is left. So as the genre went multiplayer we see more and more time being spent on balancing units. Putting the systems in place to encourage players to build a mix of units rather than concentrate on one type.
This style of balancing is popping up in new (and unexpected) areas too. Namely first person shooters with games such as Unreal (Epic Megagames) have taken efforts to create a mix of weaponry, which are all quite different and difficult to compare. There is a pistol that is good for ranged attacks since it hits as you fire as well as being good on ammo, and a sniper rifle that is very powerful and also instant hits but is limited in ammo and too slow for close battles. Unlike Doom (id software) where the BFG 9000 was the gun of choice or Quake (id software) rocket launchers. The FPS are just starting into the trend of "rock, paper and scissors" balancing. Giving players a wide array of weaponry with different features. I expect in future versions they will take similar efforts in testing to balance out these weapons, just as the efforts we now see in balancing units for RTS.
The difficult part for me now is to explain why this is good for games. Essentially it is more fun. But it is important to analyze just why it is fun. The variety creates not just more units, characters, weapons or whatever it's being applied to, it also creates more strategies and tactics. If your enemy has a rail gun then lob a few grenades around the corner. If he's using ultralisks then send in your wraiths. If you don't like his battleship then make use of your submarine. And that's why it makes the game more fun. Suddenly there is no single and ultimate method to win. Every strategy ends up creating a counter strategy and allows players to think through tactics and boast when they undo someone's seemingly bulletproof tactic. Everyone ends up trying different things yet each has a fair chance of winning with that tactic. It's just a matter of how well it is executed and how well it applies to the opponents.
So it's important to see this is not a new method of balancing. Yet game developers are applying it in new places and more seriously. We will see similar efforts appear in more unexpected areas in time. The "rock, paper and scissors" approach is to create variety yet equality. In many ways easier to define than to do since it means long and tiring testing to find which component is too powerful or too weak and why, fixing it and then testing all over again. That's it from me. After all that thought on the subject I'm going to see if I can out do the "nuke 'em" human tactic with another high tech tool in Starcraft (since rushes bore too quickly).