This allows you to map a computer to a printer – this means that every user logging on to this system will get a specific network printer assigned. Just think about a conference room and a central workstation including a special printer – this would allow you to cover this.
GPOs can do something similar, but I came across circumstances where it was easier to do this on a simple computer 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 users will bug you several times about a specific printer on a specific workstation.
There is a difference between Windows Vista and newer and Windows XP and older for the printer assignment as well.