Originally introduced as a Bitcoin Improvement Proposal. It was introduced in Bitcoin wallets which use deterministic entropy (repetition) to generate some 10,000 seed phrases from a single master seed. You could just backup that master seed, and use the deterministic entropy derived child seeds in different Bitcoin wallets. The child seed cannot be traced back or reverse engineered to the original master seed or between child seeds.
Similarly, if we generate a master seed and then generate one child seed and it’s pubkey/hex for nostr social clients, another for other nostr clients in future like a signal messenger like client, Reddit client etc. This way the master seed can be safely coldstored on a hardware wallet and backed up. You can rederive childseeds and just recall the index numbers.