Act as a senior React developer with 5+ years of experience. Explain how to use the `useEffect` hook in React for [BEGINNER/INTERMEDIATE/ADVANCED] learners, focusing on [DEPENDENCY ARRAYS/CLEANUP FUNCTIONS/CUSTOM HOOK INTEGRATION]. Provide a step-by-step example demonstrating [FETCHING DATA/SUBSCRIBING TO EVENTS/MANAGING SIDE EFFECTS], and clarify common pitfalls like [INFINITE LOOPS/MISSING DEPENDENCIES/UNNECESSARY RE-RENDERS]. Use [CODE SNIPPETS/DIAGRAMS/REAL-WORLD ANALOGIES] to enhance understanding. Keep the explanation concise but thorough, tailored for [SELF-TAUGH DEVS/BOOTCAMP GRADUATES/CS STUDENTS].