What I do not understand why delete event boxes? what need is there?
Maybe you want to keep the box and choose later some boxes Daevanion selection skill chest or any other options, not to be force to something.
Let's say, you did all your stigmas +9 or +12 or +15 and you don't need anymore stigmas, but you want to keep box and help 1 of your friend or sell it via kinah. Or you want to choose Daevanion selection skill chest (your last skill is +14, who knows) (this is all about it)