Crafting quests like for example "Craft 100 Stone Barricades" and if you want the quest to take the item away after crafting, if a player has a full inventory of random stuff, then the item gets ejected out as it crafts and yet counts towards to quest.

So essentially a player can make 99 stone barricades, the quest will count 99, pick up the 99 stone barricades from the floor, and recycle them to get the stone back, and make one more stone barricade to finish the quest using essentially 1 stone barricade. 

While most players dont care about stone in the servers that use this, it gets worse with servers that use the crafting quests for things like Craft 10 autoturrets.