chewie, crew skills are like professions/jobs in other mmos. They're gathering/crafting skills used to make money and/or gear, some of the mission skills have other benefits, like Diplomacy getting you light/dark side points, Slicing providing new recipes, and Underworld Trading giving you companion gifts. Slicing isn't needed to 'slice' things in the normal game, it just allows you to send your crew members on slicing missions to gain money/recipes, and it allows you to 'loot' sliceable objects in the world for some extra cash.