Bundles are the template to set some rules for your campaigns. You can create one bundle and use that bundle for multiple campaigns. You can create multiple bundles inside FBAS and use those bundles for campaigns.
While creating the bundle you will have all the settings you have in the Facebook campaign setup. You can see campaign objectives, bid strategy, etc. Also, the cloaking setup also gets done in Bundles.
You don't need to do the campaign setup every time, Bundles make it easy for you to do the setup one time and use those rules multiple times.