IPv6 Lo. for 6PE/6VPE

Hello, I was just wondering , while I'm planning my network to support 6PE/6VPE why should i assign an IPv6 for Loopbacks? Maybe it's needed for Point-Point links or external interfaces between my peers, but anyone here know why i should assign IPv6 for all my Routers inside my ISP if we will run PE/6VPE not dual stack. BR, Mohamed