Animation Baker helps you to convert animations
retargeted by Mecanim into Unity legacy animations. I.e. you can
retarget any animations from some humanoid characters onto your
character through Mecanim as usual and bake resultant animation into
Unity *.anim file in order to use it with legacy animation system.
As the title and description says this will retarget your mecanim anims to the legacy .anim format for you. If you are interested in using the Legacy system this tool will let you have more choices when animating your characters. You no longer need to rely on the creator of the model to make quality animations or hire someone to do so. You can just buy mocap animations instead and convert them for your model.
I have used this on a previous project and its a nice tool to have when using legacy. But in my opinion mecanim is honestly better than legacy.