Question

what is the effect of reducing friction on a machine

Answer 1

Efficiency is relate to energy conversion performance. A system that can convert energy entirely and completely into energy of another form performs the conversion at 100% efficiency. (Example: PE to KE - ideal spring mass, ideal pendulum, etc)

Friction converts useful/mechanical energy into heat.

Recalling heat engines, the Carnot cycle and the 2nd law of thermodynamics, you can't recover all the mechanical energy from the heat energy produced.

Since the heat produced by friction cannot be used to recover 100% of the mechanical energy that was converted into heat, the effect of friction is to reduce the (energy conversion) efficiency of machines.

Whenever energy conversion is involved in a real system, you can't win and you can't even break even due to losses like friction, turbulence/mixing, diffusion, etc

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