Is energy always conserved?

The definition of energy is not something as straightforward as it may seem. What is gravitational potential energy? It is a construct we made up, that works to make predictions.
Given that the expansion of space time also follows symmetric laws (it could as well contract without the laws of physics changing), could we define a sort of space-time potential energy that accounts for this "energy loss"? Does this make sense? Would this be useful at all?