A variety of reasons for this project, but first is to reduce the load of bees after the summer honey flow from production hives to prevent swarming and in turn boost weaker nucleus colonies heading into fall.
Another use is to aid in EFB. ..... if you need a detailed explanation, search youtube videos on shook swarm and EFB.
One last use is to take small loads from many colonies and then scoop bees into mating nucs with a queen cell...just too many reasons not to make one>
https://www.youtube.com/watch?v=Wv3tZ3dFUDI