The main advantage of the applicant tracking system is that the business knows what type of person applies for the job and how many accept employment if it is offered.
An applicant tracking system is used to track the recruitment and hiring process. It basically does what the name sounds like. It tracks who applies and what happens to them.
You need a Human Resources Information System (HRIS), which is a computer program for "assembling and processing data" related to managing human resources (eNotes).
The HRIS coordinates with your applicant tracking system. For example, if your typical applicant does not have the minimum requirements you’d like, you can find that out. Then you can also find out why. If you do not track your applicants in some way, then how will you know?
[A]pplicant tracking system[s] [in] analyzing and coordinating recruitment efforts - managing the conceptual structure [of] human capital. (Wikipedia)
This is especially important for large corporations. Let’s say I get an applicant for a position whose qualifications make the applicant better for another division of the company. If you have an applicant tracking system, you will be able to refer the applicant to the other division that needs him, or the other division’s human resources director might be able to look at your applicant. This benefits the organization overall.