Another take on this, which isn't so much about our use of the formula, but instead about its very existence.

E=MC^2

The equation (The 'mass energy equivalence' equation), discovered by Albert Einstein, explains (amongst other things) the energy released in nuclear fusion and fission reactions like those that power our Sun.

If this formula didn't exist, there would be no life. Anywhere.

There would be no Earth, Mars, Venus, or Mercury since every element heavier than Beryllium was created in the nuclear furnaces of stars. The universe would be filled with billions upon billions of slowly cooling balls of hydrogen and helium.

I'm pretty thankful the equation holds.

On a lighter note, E=MC^2 also tells me (assuming I didn't screw up the math) that my body mass is enough to power the entire planet for a little over 49 seconds. I'll leave it as an excercise for the reader to determine if I need to lose weight...