When you delete a group, all users that were a member of that group will automatically lose all user right privileges
assigned to that group. Be very careful to not delete the wrong group. I would recommend to not delete any of the default groups, and only delete groups that you created and no longer need.
I would highly recommend that you create a restore point
before adding or deleting groups. This way if you make a mistake and delete the wrong group, you will be able to do asystem restore
at boot and select the restore point to undo the mistake.