When you download textures from model / texture websites, the texture set typically doesn't match what you need in Unity. You can use this utility to re-pack the texture set so that it matches the Unity default shader configuration.

Here's how it works:

1. Open the Editor Window
2. For each Output channel, select an Input Texture or pick a default value (Range: 0->1).
3. Pick the Channel you want to rip from the Input Texture
4. You can invert the channel if needed
5. Bake and save.

Pretty easy, works, nice little utility.