Suppose you've got a million books and you want to transmogrify all of them, and transmogrification takes somewhere between 5ms and 1s. You might hop into a console and do:
Only problem is that locks up the console for a long time and you have to figure out some out of band way of tracking progress. Well, here's a pretty low-tech, but nice, way around that:
Now you can do
done.size whenever you want to see how far things have progressed. Crude but effective!