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If you check the default set check box, all customers that does not have a feature set granted will be configured to use the default feature set.
Once you have created one or more feature sets you will get the option to grant them to customers on the customer edit page. (If no feature sets is created this option will not be available)
You can also grant feature sets to individual users on the user editor page. (If no feature sets is created this option will not be available)
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