Speeding HDD is a feature very similar to RAID0/1. In the BIOSes of ASUS's more enthusiast oriented boards, you will find an option called "Speeding HDD." To use this feature, you must connect 2 identical HDDs to the two designated SATA2 ports. These two ports are tied to a Silicon Image Controller.
There are two modes available for this option. The "Super Speed" mode works like RAID0. The "EZ Backup" mode works like RAID1.
One would think that this may be an easier-to-set-up alternative to RAID0/1 for the average users. However, it did just the opposite. You cannot designate the "Speeding" device as boot device. Therefore, another device is required to boot, as a result making things more complicated.
Unless you are running out of SATA ports to use. I don't see how you would need this feature. Intel CH10R raid is better and more flexible.
This is all on the top of my head and I am really tired from work. Feel free to correct me.