Spankym, I would want to use my NTP service because its local. it has higher reliability and lower latency. Its also a stratum 1 and not a 2 or 3 like some of them on the NTP.org options or time.google.com. Mine also support PTP services for higher accuracy, so why not use them?
Also since I have thousands of devices already pulling NTP, I want to limit as much as possible any more use of my WAN connection than what is needed. When you get into larger networks, security and bandwidth conservation become a necessity for hosted or remote accessible service offerings so that bandwidth, buffer packet rates, and system resources remain optimal.