An advantage of James watts engine was that

Although Watt invented and improved a number of industrial technologies, he is best remembered for his improvements to the steam engine. Watt's steam engine design incorporated two of his own inventions: the separate condenser (1765) and the parallel motion (1784).

Steam engines were already in existence, mainly being used to pump water out of mines. James made important changes to the design, increasing efficiency and making steam engines cheaper to run.