Beyond being able to swear, obviously.
A long time ago, when you decided that you liked foreign languages, you thought one of these would be useful and probably bought one.
But quickly realised that searching for words you don't know online is actually a lot quicker.
While you may never open that dictionary, you know that remembering vocabulary is the hardest thing in the world. But that swear word you learnt when you were 10 has never been forgotten.
You also now know the shortcut to every accent.