You can be a mate to your staff but you need to be able to separate what is business and what is personal , you also need to be able to instil that in your staff, which isn't particularly easy and get's more difficult the larger the staff is because it introduces far more variables in personalities that need to be taken into account and managed.
Being a "tough boss" is far easier, and requires far less people skills, and so is often the preferred choice of managers with less experience. Fear is a great motivator particularly over the short term, and is better suited to work that people don't want to do, however instilling desire and inspiration and a sense of belonging to a team is better suited to positions where people can actually enjoy their work, and will reap greater rewards over the long term. As always balance is key.