Using RFC1918 on Global table as Loopbacks

Hi, I have recently encountered some operational differences at my new organization that are not what I have been exposed to before, where the loopback of the core network devices is being set from RFC1918 while on the global routing table. I'm sure this is not a major issue but I have mostly seen that ISPs use global IPs for loopbacks on devices that would and hold global routing. My question is, what is the most used or recommended way to do this, if I continue to use RFC1918 I will save some very much desired public address space, but would this come back to bite me in the future? Kind regards, Javier Gutierrez,