Single GUP vs Explicit GUP

Hello,

as I understand since 12.1 RU2, Explicit GUP permits to map a GUP regardless subnets and Globallist.xml, and without assigning any GUP in this group (Single GUP option needed for that). Single GUP forces clients of this group to map this GUP regardless subnets and Globallist.xml, and assigning the GUP selected in the option.

=> What is hte real difference between the 2 options excepted the GUP assignment ? if these 2 guarantee that clients won't go on another GUP even if on the same subnet of my clients, but only on the one in the LU (Explicit or Single), I don't understand...

Thanks in advance for your help.

Regards