I've seen a small variety of specific uses for expression columns and they seem very useful, but to be honest they haven't struck me as a solution to anything that I'm trying to do. So, really, this post is just out of curiosity to see what some of the more advanced MC users use expression columns for. I'm really looking more at the end use more so than the expressions themselves (unless they're really key to understanding the purpose).
So... any sharers? -JB