What is the employee's purpose of going on informational interviews?

One purpose is to become known to as many employer networks as possible. Secondly, you may learn more about how companies in your field operate. However, you need to have a good agenda and great questions since the people you meet with do not have a lot of time to explain from the beginning. I did get one job from such an interview, but I understand that is rare. Unless you are in management, most large employers have an HR department that operates fairly using an application process.