Provides a quick way to junk the lowest vendor buy back priced grey item in your bags.
If you want to have it learn new items prices you may find while playing, you should also install ItemDataCache ( http://wow.curse.com/downloads/wow-addons/details/item-data-cache.aspx ).
This requires a LDB display addon to work. If you don't know what that is, or don't have one yet, I have been using ButtonBin, so you may want to try that out as well.
( http://wow.curse.com/downloads/wow-addons/details/button-bin.aspx )