The fact that you can empty a barrel is something that is useful. It saves having to fill and empty a bucket 10 times.
However, the button is far too prominent, and I've just accidentally clicked it for the 3rd time this play session, emptying a full barrel of rather high quality swill. Not the biggest loss, but every time I open a barrel and see that button, it makes me nervous of clicking it by accident.
Perhaps a "Are you sure you want to empty this barrel? All contents will be permanently lost." pop-up prompt appears when you click an empty option. I remember having done the same thing with buckets in the past, and doing it with the much larger barrel would be even more swear worthy.