What would really happen to "Quantum Fusion"

[cprise]

13. Perhaps Mr. Fusion itself is efficient

but everything else that it powers could become increasingly inefficient and/or people will find more and more ways to increase their activities as more power comes online in a geometric progression. It's between that, and whether population and consumption patterns level off. The thing is, with unlimited energy, any one factor by itself that does not 'behave' would spell catastrophe.

Here are a couple explorations of scale that I found interesting:

http://physics.ucsd.edu/do-the-math/2011/07/galactic-scale-energy/
http://physics.ucsd.edu/do-the-math/2011/10/why-not-space/