CG Channel has bring a very nice review and description of functionality and advantages of Spotmask.

Please read the full CG Channel Story at:

3d-io has released Spotmask: a new 3ds Max plugin that promises to shake up the way mental ray users make adjustments to their work during post-production, particularly to animations.

The plugin, which supports both distributed and network rendering, adds a set of mental ray render elements designed to help artists manipulate rendered output more precisely in a compositing package.

Spotmask Velocity comparison