Today its more common to have casuals who get told when they have to be there and those who are told that are scheduled to have more of them there when more customers show up etc.
And it can be quite aggressive too. One of our supermarkets which opens at 7am only had a couple of staff there at opening time, one the manager who presumably opened up. And they didn't open the self checkouts until much later, usually around
9am, so they didn't have to have anyone supervising those who was mostly just standing their twiddling their thumbs waiting for anyone to use a self checkout.