1) to clean under your fingernails (I don't think I've encountered a better tool for doing this, the things you can buy specifically for this job are too pointy and hard. )
2) to lever the keys gently off your keyboard when you have dropped tea in it and need to wash them.
3) to clean your teeth
4) to nibble at when stressed, safe from the risks involved with nibbling at the actual end of the pen. That can end in a mouthful of ink...
5) to suspend your pen on things (I suspect this is the official reason for them, but other brands of pen have lids that only do this one thing, not all the rest).
6) I am pretty sure you could blow through the hole and make a small whistle, but so far have failed to achieve the correct embouchure.
Oh dear, it's Friday... I must do some work. I really must.