The phrase is taken literally when discussing the actual weight of objects or persons.

Literal Weight

Avoid exaggeration; use it for actual weights, not to express that something is heavy or light metaphorically.

Exaggeration Avoidance

It's often used to highlight when something weighs a lot or more than expected.

Use it to signify a small factor that changes the outcome or balance in a situation or decision.

Implies a pivotal factor or moment that shifts an undecided situation in one direction.

When used in an idiomatic context, it has nothing to do with actual weight or scales.