If you havent been forced to discard on a bad roll, youll either get back a random card from your graveyard or draw two
Since we're in the midst of prerelease season for Guilds of Ravnica, I've been doing the same things that you probably are: inhaling preview cards on the Intarwebs, reading through set descriptions and reviews, and trying to figure out which guild you're going to play or which card you really want to open (note: it's Assassin's Trophy...that card is gas, kids)
This is obviously designed for Life Gain brews where this is a nice tool, and they are even more popular, coming in second-most at EDHREC.com, only coming in behind the generically named artifacts
It's primarily a bar for patrons throughout the Sector 7 slums to visit, but it also contains a secret room as well
(1 Artifact Tap, Sacrifice Nihil Spellbomb: Exile all cards from target player's graveyard
And members often have rare and hard-to-find cards available