All limbs had their charge cost reduced by 1? So arms and plantigrade legs would just be played by themselves, while big arms and digitigrade legs would cost one card face-down? This puts the Arms and Big Arms on the power curve (1 card played : 1 cog of action), while putting Plantigrade Legs and Digitigrade Legs squarely above it at 2:3 and 1:2 respectively.
Similar cards above the curve include the Turret (1:2), Master Crew (2:3), the Macro Gun (2:4), the Capacitor (1:2), , Plasma Shotgun (3:4), the Laser Blade (3:4), and the Rocket Pod (2:3).
Systems on the curve would be the Initiate & Adherent Crew, the Extra Armours, the Sensors, the Deflectors, the Shields, the Gun Battery, the Hand, the Claw, the Laser Battery, the Plasma Howitzer, Macro Laser, Buzz Saw, the Sponsons, the Jump Jets and Thrusters. All 1:1.
Systems below the curve would be the Vulcan Gun (2:1), at the low end. However, there's a potential (1:3) involving operation with a Master Crew and Initiate Crew.
It follows, additionally, that all systems on the curve can be pushed above it with a Master Crew. With just a Master Crew operating it, a Vulcan Gun might achieve a (2:5) depending on positioning, but minimally 1:1.
Why though? Aside from the obvious 'feel good' of making it easier for the Titans to move, turn, and fight, the limbs' combined actions are some of the most common actions in the game. It also makes for a better, more defined offset in the most efficient option vs the most efficacious option. Playing a capacitor card is less straightforward too.