When and why to use Speedgrade? I read both of these questions which came up in my search for Speedgrade:


Tips to make professional looking hand-held videos using smart phones?
Adobe CC Post-Production Workflow (Story, Prelude etc.)


But I'm not seeing any broader question about Speedgrade. For making promotional / instructional videos that will be uploaded to YouTube is it necessary to use Speedgrade and what exactly does it do? Should I only use it everything is live action? Some of the videos I work on have a mix of live action footage I take with a Canon 70D as well as Flash Animation.
You ask what it does: Speedgrade is a color grading / correcting tool. Davinci Resolve is another, and there are others still. They allow you to adjust the characteristics of a video on a shot-by-shot basis.

It's never necessary to use any color grading tool, but you'd do so when you want to match scenes from different sources or shot under different conditions, or to give your video (or one portion) an overall look. The usual use is for consistency.