The 787 Dreamliner family uses more efficient engines and lighter weight to cut fuel consumption. That's important for airlines that have to deal with fuel costs and with exhaust that worsens global warming.
The Boeing 787-9 can use either General Electric or Rolls-Royce engines. The test flown over Farnborough, the first Boeing built, comes with Rolls-Royce engines. The scalloped cowling cuts down on noise.