People are wasteful. It's why we need a mantra like "reduce, reuse, recycle," after a century or two of "consume, throw out, set on fire."
We're also generally content to keep doing things the way we've always done them, even when that way is dumb. So over time, we made a system that can provide us with heat, and we made another system that can provide us with electricity, and we just plodded along, running these two separate systems, living our dumb human lives.
And then a few people wised up, recognizing that we could combine these two systems into one: cogeneration, or combined heat and power (CHP). Make gas hot, spin a turbine for power, use the hot gas to heat up (or cool off) a building. Maximize the efficiency of a fuel source. Less waste, less being dumb.
Here's how such a system works. (Apologies in advance; this was literally the most interesting video I could find.)
Such a system would be cool to have in our houses, saving energy costs. But in massive industrial facilities, huge rooms that use a ton of power, the efficiency increase could be enormous.
Which is why President Obama today signed an executive order that aims to vastly increase the use of CHP systems in industrial facilities.