I'm confused why it matters. If I heat something with 2J of energy and it released 1J of energy, it's like the matter has been heated with 3J of energy. If I ca

I'm confused why it matters. If I heat something with 2J of energy and it released 1J of energy, it's like the matter has been heated with 3J of energy. If I can extract heat energy with 80% efficiency, I can extract 2.4J, more energy than was put in.