What is the meaning of “mechanical advantage”?

The meaning of "mechanical advantage" is: "(noun) the ratio of the force produced by a machine to the force applied to it, used in assessing the performance of a machine".

Presumably that the mechanics of the situation are superior for one thing over another.  Mechanics refers to how things work, the actual details of the function.  Efficiency and effectiveness, the things likely to be seen as advantageous from an operational standpoint, are often not at all equal when comparing different physical systems and//or methodologies.

That depends VERY much on the context.

Examples showing DIFFERENT meanings:

Bob has a tank, Rob has a spear. Bob has a mechanical advantage over Rob.

Bill's racing robot has a three-gear transmission; Will's has a four-gear transmission. Will's robot has a mechanical advantage over Bill's.