Newcomen's coal-powered engine heated a boiler and filled a cylinder with steam. It then sprayed cold water into the cylinder to condense the steam, creating a vacuum, which pulled a piston down.
One cylinder did two things.
Watt's engine moved the cooling/condensing to a separate container. The cylinder stayed hot. The condenser stayed cold.
For the same output, Watt's engine required about a quarter of the coal of Newcomen's.
Isolating the chambers meant less waste.
In AQR's 2020 paper, The Tax Benefits of Separating Alpha from Beta, researchers separate the market and alpha components of an investment portfolio and find similar results.