In newer versions, guest customization technically runs as long as it's enabled.
every boot, we check for a flag in the VM settings (needs guest customization).
if no, then don't do anything.
if yes, it's one of 3 reasons.
1. it's a brand new VM and never customized (full customization via SysPrep required or the shell script)
2. you added a NIC, changed networking, changed Computer name. This is a delta customization, only when needed
3. Force customization ... when a user changes the IP and complains that something broke.