Advantages of full install via iTunes:
- Device will be synced and backed up automatically during the update process
- If at location without wi-fi access (and without an unlimited data plan), won't use up (large?) portion of the monthly quota
- Device will be charging during the update
Disadvantages of full install:
- Tethered to computer for the duration of the update (unless using Wi-Fi Sync)
- Full update could be significantly slower due to the large upgrade file download
Advantages of delta update via Settings:
- Convenient - no need to be tethered to a computer while updating
- Delta updates are smaller - with potentially shorter total update time
Disadvantages of delta update:
- Users might not backup devices if prior to running the delta update - a potential issue if the update fails
- Update process might use significant portion of the device's charge on the battery, running risk of corruption if the battery dies during the update
- If device isn't at 50% power, the device can't be updated via the update process unless plugged in (per this article):
To install these updates, however, you need to have at least 50
percent battery life on your device, or have it plugged into a power
source.
I'm sure this list isn't comprehensive, but contain most of the issues that I can think of.
