Open Battle.net is Blizzard's gift to the hackers and cheaters. As mentioned, characters on open BNet are stored on your own hard drive, so you can edit their stats and items to hell and back. You can also play modded games, which is very fun. It's fun if you're playing with people you know, but unlike the realms (closed Bnet), it's not fun to just join a random game. Rather than wanting to play the quests, most people on open BNet want to duel or show off their hacked items.