The maximum number of quests that can be acquired is 40, however if an automatic quest occurs, the number can temporarily increase to accommodate it. The button allows a quest to be shared in a group or alliance, if a quest is shareable. The button can be used to abandon a quest, with the exception of Campaign quest which cannot be abandoned, and a few others. Abandoning a quest may or may not removed associated Quest Items from inventory, so it is a good idea to check.