Like NextGEN albums, the tag albums feature provides a quick way to create a group of tag galleries. Each tag you specify will become an automatic tag gallery in your on the fly tag albums. It behaves exactly like normal albums - the navigation is aided by breadcrumbs so you can go back and forth between tag albums and tag galleries. Interestingly, this feature is no longer part of the NextGEN Gallery and the only thing that comes close to it is the tag cloud. Still Justified Image Grid makes it available in a form that is even better, because you can see a preview image for each tag before opening its gallery. Tag albums are most useful when you have less/no overlapping tags.
On the fly tag albums that open tag galleries on their unique pages
If you open a tag gallery from this tag album, it'll work exactly like normal NextGEN albums - the thumbnails will open on a new page.