Not the parent, but all other things remaining the same, population growth alone will drive the need for more cashiers. Since ATMs did not stop population growth, percentage based metrics help account for that.
So the different types of numbers can help drive home different points:
* in absolute numbers, ATMs didn't cause any job losses.
* in relative numbers, there are less job opportunities in this space. (e.g. there used to be a need for 1 cashier per N people, not there is only a slot for 1 cashier per 2N people).
The second type of thinking is what people are worried about - if we keep reducing percentage of people who are needed to do stuff, what the other folks do?
I think the second is actually much less worrisome than the first. With absolute job losses, people who lose their jobs need to retrain or accept (probably much) lower pay in different fields. Both of those are hard on people psychologically, and requires very expensive government intervention to mitigate. With the second you just alter the mix of what young people are trained in originally. It will be more expensive to train a young person in programming as opposed to truck driving, but it's not nearly as bad as training a 50 year old trucker in programming, fiscally or psychologically.
There's also the factory vs car improvement difference. Factories did not make workers obsolete; cars did make horses obsolete. I'm not sure we can ahead of time tell whether particular technological improvements are more like factories or cars.
So the different types of numbers can help drive home different points:
* in absolute numbers, ATMs didn't cause any job losses.
* in relative numbers, there are less job opportunities in this space. (e.g. there used to be a need for 1 cashier per N people, not there is only a slot for 1 cashier per 2N people).
The second type of thinking is what people are worried about - if we keep reducing percentage of people who are needed to do stuff, what the other folks do?