The Snapshot option is for saving all parameters to look at later on (drive parameter S-0-0017). Commision is for backing up all operation data (S-0-0192) and Device firmware. This is useful for serial commissioning of devices. Device replacemnt backs up operation data, firmware, and retain data (p-0-0195) in case you have to replace a specific device.
See the image below for a breakdown chart:
