Okay say you own someSmallSite.com. Its NS nameserver, is say,
ns1.hostgator.com. The NS server of Hostgator is
ns1.p13.dynect.net. The NS record of that is
ns0.dynamicnetworkservices.net which has a same (glue) record of the same domain.
Say someone tries to resolve someSmallSite.com. Since it's a small site, most DNS servers probably have no caches of any of this. So 3 round-trips would have to be made in order to find the actual authoritative DNS server for someSmallSite.com. (resolving
ns1.p13.dynect.net and at the end,
ns0.dynamicnetworkservices.net which will contain the actual IP address of the DNS server).
If you, instead, make glue records for someSmallSite vs. using the DNS of a shared host (like Hostgator), aren't you avoiding 3 round-trips to resolve the NS record, and then the NS record of the NS record etc, until you finally get the IP address of the DNS server?
If my logic is correct, would this mean that adding a glue record for a small site would be more beneficial in practice, than, say, a big site, which prob has all of these NS servers already resolved in the cache + they are more likely to be on a DNS server which has the IP glue records immediately vs. pointing to another DNS server which points to another etc.