React's key prop isn't just a warning suppressor - it's how React keeps track of elements between renders. Without a unique key, React might reuse the wrong elements, causing bugs or flickering UI. The key should be stable and unique - avoid using array indexes unless you have no choice. When you dynamically render lists, like with .map(), always include a key to help React efficiently re-render only what changed. Ignoring this leads to subtle and painful bugs. Want clean, performant React code? Respect the key prop - it's small but mighty.