If you are selling a PC or an external drive, a standard format can be undone by recovery software. An LLF ensures your data is gone forever.
A single-pass zero-fill on an HDD makes data unrecoverable by software. Only a hardware lab with platter reading might retrieve fragments. For SSDs, Secure Erase is equally effective. Do not believe myths about needing 35 passes (Gutmann) – that was for older MFM drives with different encoding. hdd llf low level format tool full updated