What occurs when a save-config command is issued?

Issuing save-config (tmsh save sys config) serializes the active running configuration held in memory to the BIG-IP configuration files on disk, effectively backing up the current state so it survives reboots and can be restored or referenced later.

Syntax verification followed by installation of a configuration into the running system describes a load or merge operation (load sys config), not a save; save-config writes the existing running state to disk without re-parsing or reinstalling it.

Loading configuration files from disk into memory is the function of the load-config command; save-config performs the inverse operation by writing the current memory state out to disk files.

Saving to a compressed archive format describes the save sys ucs command, which creates a User Configuration Set file; save-config writes standard flat configuration files, not a compressed or archived bundle.