Difference Between sourceMapRootpath and sourceMapBasepath?

The grunt contrib less plugin has two similar sounding properties with similar descriptions.

sourceMapBasepath : Sets the base path for the less file paths in the source map.

sourceMapRootpath : Adds this path onto the less file paths in the source map.

To a layman these descriptions sound essentially the same. Could someone please contrast these two properties, possibly with a use case for each?