**Advantage**: Avoid recomputation. Same DF used multiple times = one compute, many reads. Critical for iterative algorithms (ML), multi-action pipelines.
**When**: (1) DF reused 2+ times. (2) Iterative (e.g., loop with same lookup). (3) Small dimension joined repeatedly.
**Storage Levels**: MEMORY_ONLY (fast, evictable), MEMORY_AND_DISK (spill), MEMORY_ONLY_SER (smaller). Cache = MEMORY_AND_DISK.
**Why Care**: Recompute of 1TB = hours....
The complete answer continues with detailed implementation patterns, architectural trade-offs, and production-grade considerations. It covers performance optimization strategies, common pitfalls to avoid, and real-world examples from companies like Tredence. The answer also includes follow-up discussion points that interviewers commonly explore.
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