Guide Talk:Skyrim Installation
From Step Mods | Change The Game
Steam backups without Data directory
Under the Steam section when discussing backups, it is mentioned to omit the Data directory to save time and space. It should be noted that the Data directory contains the largest files that are required for a virgin Skyrim installation. To not back up the Data directory will significantly add to the download time should one clean their install and attempt to recover from that backup.