Do transistors lower power consumption in circuits?

[NewtonianAlch]

I'm just looking over some introductory notes to transistors and it says that BJT transistors are useful for amplifying current, so does this mean that power consumption (P = VI) in a circuit would be reduced because of a smaller input current?

Or is the power consumption calculated by the output current from a transistor?

 

[Studiot]

You are studying BSc Electical Engineering.

Surely, power consumption = total power drawn from the power supply.

Of course, some of that power is supplied to the load and some is wasted in circuit inefficiencies.

So perhaps you would like to think again about your question?