I’m kind of a stickler for a clean hard drive, especially since I started using Macbook Airs a few years back, what with their tiny little SSD units. I’ve moved most of my music to the Cloud and my iPhoto library to an external hard drive, but there’s still a ton of cruft that ends up on my system.
So, once a month or so, I sort my Movies, Applications, and Downloads folders by size, and delete the biggest things I don’t need anymore. Or I move them to an external hard drive for access later.
What I’ve never done before is use Spotlight to find these files easily across all my folders.