I am new to using MapInfo 12 and have recently noticed the convert to regions and convert to polyline function.
What is the difference between a region and a polygon?
In MapInfo, regions include the set of polygons, rectangles, and ellipses. Don't ask why they consider rectangles to be a special type of polygon, I'll never figure that out.
However, I think you've misread the tool. It actually says "Convert to Polylines."
See this post for more information about MapInfo Map Object Types.