In so doing they are able to keep people out of areas they aren't authorized to be in, and if there is a problem they are able to determine who was in the area at the time. Many of these same organizations will allow anyone who sits down at a computer to wander anywhere they want to on the network or on the local hard drive, unchecked and unmonitored. Users are able to run or even install programs, visit websites, and copy, modify or delete data. Unknowledgeable users can wreak havoc on a system while attempting to install their own software or fix an existing problem. These are the sorts of questions that should be asked when determining security needs.
All data is sensitive to some degree, exactly how sensitive is unique to each environment.
In many organizations the loss or exposure of a corporate officer's contact manager could be catastrophic. Lack of adequate security can compromise the ability of organizations to perform their mission. Accidental modifications performed by well-meaning users can lead to data loss or inaccuracy and downtime for the individual PC or the whole network. All occurrences of this sort lead to significant increases in Total Cost of Ownership of IT resources. A directed attack by an insider with specific goals or objectives can have far worse consequences.