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You'll find lot numbers on all manner of things that are not individually serialized but where tracking a potential screw-up without having to recall EVERY item made is important if something is discovered later on.

It's important in the reloading world. Sometimes powder burn rate can vary slightly from lot to lot. Usually not enough to matter but if you're playing around with max loads it might or doing benchrest level precision or if you're building powder puff loads for action pistol shooting that must make a certain velocity times bullet weight score.

On the accuracy end of things it's nice to have each component in a batch (case, primer, powder, projectile) from their own lots because they are more likely to be more consistent and therefore more accurate.