Hard Drives and Data

An article was forwarded to me discussing how old hard drives are purchased by individuals and then they can pull information from the drives because the data wasn’t removed. And then the discussion continued in the office and others about using third-party software to destroy the data prior to tossing the drive or selling the drive. But why use third-party software to do this when the utility “fdisk” is available? Once the partition is deleted, isn’t all the data along with the MBR deleted?