What are the disadvantages of friction?

Well, for starters, it produces heat inside machines and such, and second, it makes us use more power when friction is applied. Third, it opposes the motion. Fourth, noise is also produces. And finally, it makes engines consume more fuel.

Efficiency is an action of doing something. for example when you take a test. good efficiency means you did well but bad effeciency or no effiency means you did bad.