A sense of scale.
It’s terribly easy to get lost among strings of zeroes. As we endlessly see with the papers confusing billion for million etc.
But we’re measuring something in ounces, it’s small. In tonnes it’s large. Pints is easy to envisage, we’ve all actually seen someone holding one.
Decalitres? Sure, we can work it out but it’s not immediate in the same sense. And the number who get confused between deca and hecto litres…..
And sure it’s just an oldie casting back to something in childhood. Yet it is still an advantage in that we never do talk about one thousandth of a pound – a grain (not, actually, the same amount) gives a better mental image.