A lot of improvements were made regarding an upgrade procedure between major vSphere versions. In the past, there were two reboots. However, since vSphere 6.7, only one reboot has been required during the upgrade. That does not seem like a big thing, but when working with complex infrastructures, this can save a lot of time. Also, please note that when upgrading from VMware vSphere 6.5 to 6.7, you will experience this feature as well.