Multiple Render Outputs in action was introduced in version 2011 of Flame and Smoke.
This tool allows you to output multiple variations of a single composite so you can choose what to render. This means if you want to make multiple versions of the same composite with slight variations, you could set this all up in one composite.
You could also output multiple mattes/alphas for different parts of the composite for fine tuning at a later stage.
All good tools for great workflow enhancements!
This blog looks at the benefits of this feature in Smoke on Mac, Smoke Advanced as well as Flame (and some extra outputs exclusive to Flame)