When a sorcerer uses cursed energy it doesn't exist in a vacuum, it interacts with other forms of energy. It becomes the kinetic energy of their strikes, the thermal energy, the light energy, and other elements as a result of the manifestation of their techniques. That's why CTs are likened to appliances and cursed energy is likened to electricity; because it's meant to be treated as another kind of energy on a comparable level.

In other words, cursed energy is not ever "destroyed"; it becomes other forms of energy. This is why Kenjaku posed the possibility of using it as an energy source. Presumably cursed energy can be turned into electricity.

In regards to Gojo, I think Gojo's efficiency works like this: cursed energy expenditure is so marginal that his total cursed energy reserves aren't significantly diminished due to usage of his CT; and presumably, he can replenish himself relatively quickly as well.

Now, in regards to your question specifically, keeping these things in mind, I think RCT in general follows the principle of energy conservation regardless of whether it's Gojo using it or someone else. The principle of positive cursed energy is mathematical, where you multiply (inherently negative) cursed energy with itself to make it positive. This is a little nebulous because we do not know the exact formula for it, how much CE is on both sides of the equation, etc, just the mere principle. But it's still ultimately equivalent. If we want to multiply 2 CE by itself it would be something like:

(-10) * (-10) = (+) 100

Say this is what Gojo uses to make Red. Red is more destructive than Blue, presumably because this process of conversion is in of itself taxing. RCT in general is more taxing than regular usage of CE and that's because the conversion process isn't easy.

Still, it maintains the total energy balance inherently.

I'll answer your other question (I think it's the same anon?) here.

Could the rct be compared to symmetry in physics, where every force or particle has an opposite? Is Gojo manipulating the balance between cursed energy and its positive counterpart to reverse its effects?

It would be possible if positive cursed energy could be producted on its own, without the dependency on regular cursed energy. Like for example, if it could be produced from positive emotions. This doesn't seem to be the case. +CE seems to rely entirely on CE conversion and it doesn't exist independently, leading me to believe it's more Gege playing with mathematics (the way he does with Black Flash) than with Physics.

I don't quite understand the second question in this part, but hopefully the first answer clarifies how RCT is meant to function. Physics and math aren't my expertise, I apologize! I am the M in STEM through and through.