AutoBindOnPickup

From WoWWiki

This article or section is a miscellaneous stub. You can help expand it by editing it. If appropriate, you might want to import some information from a database site - see Fansites for listings. Pages linking here may have clues as to what the page should contain, or perhaps the discussion page.

It basically just bypasses the BOP dialog when you're soloing, so you aren't bugged by it. However, when in an group and using Free for all looting, it may be adivsable to turn off AutoBindOnPickup to avoid taking a BOP drop far more useful to another party member.