As part of my Aperture workflow, I use a Metadata Preset during Import to set the city, state, and country (among other things) for where the photo was taken. Later in my workflow, I geo-tag the photos in Places. Sometimes, I find out that the city I thought I was in when I took the photo is not where I actually was. Thankfully, using another Metadata Preset, such mistakes can be quickly corrected. The short video below gives an example.

If you haven't explored Metadata Presets in Aperture yet, have a look. They can be a great addition to your workflow.