One more part not really usefull for astrophotographers. There is 2 parts:
1. Volume Anamorphosis Correction: it allows to make cylindrical or spherical projections to your pictures. Those settings will be useful if you need to stitch some wide angle photos to realize a panorama. But, for such a case, it's better to use a software dedicated to panorama like PTGui.
2. Keystoning / Horizon: For non astro photos, those settings are really efficient to correct perspectives, for example if you have photograph a building from the street. Try to scroll the cursor, it's funny and instructive.