In Aperture, flags are my kitchen sink tool. The common theme for my usage is a flag is temporary. Since it's temporary, flags have the flexibiliy of meaning whatever I want them to for the situation at hand.

Sometimes a flag is a quick and dirty way to note an image I didn't complete a workflow step for. Other times, flags separate a set of photos from the rest of a shoot, such as for post-processing or for sending to friends and family.

In this example, I use flags to pick a few images from a sequence of images for some "tourist removal" post-processing.

How do you use flags in your Aperture workflow?