What does actual mechanical advantage tell you about a machine's usefulness?

Question

What does actual mechanical advantage tell you about a machine's usefulness?

Answer 1

Actually, how efficient it will perform on a given task.

A machine's actual usefulness may need a great deal of mechanical advantage - such as a car jack. A very large movement of the lever will result in a short increase in lift - but at a much greater force.
The greater the ratio, the lower the force necessary to raise the vehicle.
The mechanical advantage will tell you if the jack will raise the car very quickly with a moderate amount of force, or much slower with a minimum amount of force.
With this information and the intended purpose, you are able to decide which jack better meets your needs.
The same criteria holds true for more complex machines as well.

Answer 2

It tells how much effort is put into doing work, for example how fast a motor has to spin in order to generate a certain velocity of a car. Lower gears have lower mechanical advantage.

Answer 3

Generally, the high the MA, the better the machine will be.