What is the difference between hard delete and soft delete in Salesforce, and when does it matter?

A standard delete is a soft delete: the record moves to the Recycle Bin and is recoverable for a limited retention window before being physically removed.

1. Why soft delete is the default: It protects against operator error, and for ordinary business deletions that is exactly what you want.
2. Why it matters at volume: Soft-deleted records still occupy storage and still sit in the index until they are purged. Deleting thirty million records softly does not immediately relieve the storage or performance pressure that motivated the deletion.
3. Hard delete: The Bulk API hard delete option bypasses the Recycle Bin entirely. It is the right tool for large planned purges, and it requires the Bulk API Hard Delete permission.
4. The governance precondition: Because it is unrecoverable, I will not run a hard delete without confirming the records are captured in the archive, that no legal hold applies, and that the selection criteria have been reviewed and dry-run against a count. For compliance-driven erasure, hard delete is usually mandatory rather than optional, since a recoverable delete does not satisfy a right-to-erasure request.