This is perhaps the most effective type of security, because it dissuades people from attempting things on your network, as opposed to stopping their efforts. The more people that you can discourage, the better. Say that you own a business, and you have to worry about subversive employees who might exist, and be very unashamed of doing what they will to undermine the business (i.e. taking customer lists). You want to discourage them from trying this.
First and foremost, it is imperative that they know that the information here is your property and yours alone, as owner of the business. As “entitled” as a disgruntled employee might feel to this information it is not his, and serious legal restrictions come along with that.
Whenever an incident occurs, involve law enforcement. The most embarrassing thing would be to be led out in handcuffs by police officers for attempting an attack on your employers. Make sure that they know the humiliation which will come with it.
These are simply a few of the steps that can be taken to preventative security, and should be kept in mind when considering how to keep one’s files and information secure.