I think I used the math node because I also have a tendency to plug the texture into the ambient node sometimes (like, for eyes so the iris texture has an effect on the ambient glow), and the math node would allow both that and the mask.

The math node is also useful if you have a black on white image, setting it to subtract to invert the image.

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If you're joking that's just cruel, but if you're being sarcastic, that's even worse.