Some properties on the default user profile may contain information about users in your organization that you are not likely to use. You can delete some of these properties.
Some properties cannot be deleted, and the option to delete them is unavailable. This is true of system properties, and properties that are being used in audience rules. You can delete properties used in audience rules by first deleting the audience rules based on those properties.
Note If you delete a property, all user profiles with values for that property lose the associated values. There is no way to recover this information, so be very careful when deleting profile properties.