backup commands tmsh save sys ucs config-pre<changexxxx>.ucs</changexxxx>

tmsh save sys ucs ... saves what's called a UCS archive of the BIG-IP system's configuration data, including running config, all config files, license, certificates and keys, BIGDB.dat database settings, etc. It is designed to be a complete backup for a specific BIG-IP system to be used to recover from problems on that system or to roll back configuration changes. While it can be used to load configuration data onto a different BIG-IP system, you have to take into consideration the fact that it includes a license that is tied to a device with a certain serial number.

tmsh save sys config file ... saves a copy of running configuration data only on that system. It can be used to relatively easily clone configuration data from one BIG-IP system to another, or to make edits to configuration data and then reload. Since it's not a complete backup of your BIG-IP system, it is not designed to for restoration purposes, more for migrating configuration data only from one BIG-IP system to another.