I've only played a few times, and all were solo. So for my education, what is the strategical and/or mechanical benefit for doing this?
I think that the most common situation would be emptying your hand before camping. You have to weigh the time loss if you keep them in hand against wasting a turn. For example, if you're at the beginning of the mountains with only useless cards in your hands, you're probably better off spending a useless action than falling back and having to spend turns and resources on another river move.