The quality of the copper conductor directly affects safety and performance. High-purity electrolytic-grade copper (typically 99.97%+) has very low electrical resistance, so it carries current efficiently, runs cooler and wastes less energy as heat. Cheaper, impure copper has higher resistance — it heats up more, ages faster and is a fire risk.
Lower resistance also means less voltage drop over a run and better current-carrying capacity. This is one of the clearest differences between genuine branded wire and substandard product, so it is worth buying from a trusted manufacturer — see how to check you are buying genuine APAR cables.
APAR house wires use high-purity copper conductors for low resistance, cooler running and longer life. (For larger feeders, aluminium is sometimes used instead.)