Here's the simple reason why planes have winglets

Winglets allow the wings to be more efficient at creating lift, which means planes require less power from the engines. That results in greater fuel economy, lower CO2 emissions, and lower costs for airlines. Boeing claims that winglets installed on its 757 and 767 airliners can improve fuel burn by 5% and cut CO2 emissions by up to 5%. An airline that installs winglets on its fleet of 58 Boeing 767 jets is expected to save 500,000 gallons of fuel annually. (www.businessinsider.com) More...