Turbos do not make anything more fuel efficient, they simply allow you to have the fuel efficiency of a small engine off boost, and match the power of a larger

Turbos do not make anything more fuel efficient, they simply allow you to have the fuel efficiency of a small engine off boost, and match the power of a larger engine while on boost. It's still a tradeoff however, there's always some lag and delay to throttle response, extra piping and cooling hardware, and more backpressure in the exhaust means it loses efficiency compared to a naturally aspirated variant of the same engine.