is the key part: if you want to know what order to apply changes in, you need every system to have fairly close time synchronization so you can apply changes in the correct order. NTP will get you enough precision for many applications but if you get enough updates to the same resources, you're certain to start getting differences which are smaller than the reliable accuracy of your system clock.
You can use other protocols - e.g. a CAS-style "change old-value to new-value" conditional update - but those have performance implications and require app support. Given that a GPS probably costs about an hour or two of engineer-time, trying to eke a little more precision out of the system clock seems like a potentially cheap win.
is the key part: if you want to know what order to apply changes in, you need every system to have fairly close time synchronization so you can apply changes in the correct order. NTP will get you enough precision for many applications but if you get enough updates to the same resources, you're certain to start getting differences which are smaller than the reliable accuracy of your system clock.
You can use other protocols - e.g. a CAS-style "change old-value to new-value" conditional update - but those have performance implications and require app support. Given that a GPS probably costs about an hour or two of engineer-time, trying to eke a little more precision out of the system clock seems like a potentially cheap win.