watchEffect() automatically tracks all reactive dependencies used inside it and re-runs whenever any of them change — without you having to specify which values to watch. As the creator of CoreUI with Vue development experience since 2014, I use watchEffect() when a side effect depends on several reactive values and I don’t want to manually maintain a list of dependencies. The key difference from watch() is that watchEffect runs immediately on first call and doesn’t provide old values — it’s ideal for synchronization effects rather than reactive comparisons. Understanding when to choose watchEffect vs watch makes your Vue code cleaner and more maintainable.