FaceBook for BlackBerry would be one example. Since I use SocialScope, I don't really need the FaceBook app. There are a few reasons for keeping the app (it's an Official app, after all), but I don't need those features too often. That's why I use the Archive function of BlackBerry App World.
It's a pain in the hind end to download the FaceBook app every time I want to use it. Plus, downloading while I'm out and about eats up my data usage. Archiving the app uninstalls it from application memory and saves the installation files to the microSD card. Now, when I want to use FaceBook, I just install it using App World. I don't have to wait for it to download again because the installation files are already on my BlackBerry. I get all the benefits of having the app when I need it as well as freeing up memory for the next cool thing.
I could spend the next few paragraphs explaining in detail about how to use BlackBerry App World's archive feature, but that video up there does a much better job.