This is done to simulate popular launches (eg. hire people to wait in line when your new store or restaurant opens, to give the impression that the new place is

This is done to simulate popular launches (eg. hire people to wait in line when your new store or restaurant opens, to give the impression that the new place is hot) or for faking headcount metrics for investors (eg. hire people for a day when the investors come, so they can gawk at the open office full of people). It's ethically dubious, but if it's done for a day or two, it's not that expensive compared to actually hiring that many people on a full time basis.