When you're out questing you get a lot of junk. Thing is it can be valuable, especially when you're starting off. So, tell this addon how much bag space you want to maintain for important stuff, and it'll delete the cheapest trash each time you loot, pick up a quest item, craft something etc.
To see a list of settings you can set, type "/bs" in chat
Currently only deletes Junk (grey) items. Will be extending to include your own personal list of additional items later. Never get ganked while working out what to delete so you can loot that sweet blue cloak...