What Is the Benefit of Having “Child Keys” Derived from a “Parent Key”?

The primary benefit is organization and control. A parent key can generate a large number of child keys, which can be used for different purposes (e.g. different accounts or privacy).

This hierarchical structure allows the wallet to manage funds across multiple addresses while only requiring the backup of the single master seed. It also enables the sharing of a public parent key without exposing the private parent key.