I have most of my domains with an offshore registrar, and now I need a few .co.nz domains. It works out a bit cheaper to use a NZ based registrar for .co.nz domains, so that's an advantage. Also, pumping money into NZ is always good. But would there be many other reasons to use a NZ-based registrar? Maybe it would help a bit if there was a domain name dispute or something? Just a guess.