It securely erases the drive contents. This is typically used for SSDs where a charge is sent to all cells setting the all content on the SSD back to blank. This needs to be done periodically if the drive, only older ones or if the OS, does not support TRIM; garbage collection on SSDs that reallocates erased file areas on the drive. This technique is not what is used on HDs and I'm not sure if they have an internal algorithm that walks the drive writing dummy data to all sectors or if it's not supported. There are programs that can be downloaded that will do that data overwrite to HDs; repeatedly so no residual image is left of the original data. Just not sure if the HD drive itself is capable without an external program to do the writing. SSDs are capable of just self erasing securely.   

It would be nice If we could see the secure erase command incorporated in future bios version.
For that kind of board it is a must, taking into account that we see the command in cheaper boards.
I would also like to say that I had a bad experience with bios version 2.40.
I lost my ram speed, from 3200 I could only boot @ 2933. The board also became unstable. Reverting back to version 2.30 everything is working fine now.
Hoping new AGESA 1.0.0.6.a will solve more problems and not create new ones.

My specs:
AMD Ryzen 1600X
ASROCK X370 TAICHI

CORSAIR CMK16GX4M2B3200C16R (with SR HYNIX)