Tags are added to panoramas and are used to filter panoramas which is especially helpful when you have a lot of images. You can also them in the skin as triggers.
Using Tags with the Skin Editor
Filtering Images in the Tour Browser with Tags
Using Tags to Filter Levels
Tags can be added to each node in a tour to signify a specific level of a multi-story building. This is useful for tidying up the tour browser or for when adding levels to a Google Street View tour.