Are iridium spark plugs worth it over copper or platinum?

Mechanic-community consensus on r/MechanicAdvice is that iridium plugs hold a sharp electrode edge longer than platinum or copper, which translates into longer service intervals (often 60K–100K miles) rather than dramatic horsepower gains. Copper plugs are cheaper but wear faster and can cause harder starts as the gap widens. For most modern engines that came with iridium from the factory, downgrading to copper or platinum is generally discouraged in those threads.