Okay, it allows you to wear two extra weapons. So what? What does it do beyond that?
Doublesheath?
When you're disarmed you automatically draw a new weapon, and it helps you hold more rares. And you can use the draw command to swap weapons sets for different situations.
It does nothing, especially for rogues.
WC
Depending on your class, the benefits differ. Rogues love doublesheath for a different reason then warriors/rangers love it, which is different then why a BLM loves it (though it is mostly the same between warriors/rangers and BLM, with the difference of a quicker switch from 2h to dualing)
Circle with a double sheated rare dager, will give side step attack.