When you have whites that border into blown out you would pull down the Recovery slider. When you have blocked out, muddy shadows you would pull up the Fill Light.
Why not just try them on some images and see what they do? Then next time you can begin to intuitively know what they'll for your image.
Of course, when you upgrade to Photoshop CS6 you'll need to forget all that. It's all different. No, I'm not kidding.
media kat wrote:
I've been working with Temperature, Tint, and Exposure. When would you adjust the Recovery and Fill Light?
When I've exhausted the possibilities of PV2012!