This allows you to map a user to a printer – it would work like a follow me and connect certain printers to certain users.
GPOs can do something similar, but I came across circumstances where it was easier to do this on a simple user level. There is no group-based assignment in between – you can adjust it if you want. The idea is to have coverage for those special situations where this will make your life easier and avoiding that the user will bug you several times.
There is a difference between Windows Vista and newer and Windows XP and older for the printer assignment as well.