Why do companies need to have an "apply online" or "deposit your resume" portion on their website?

I'm a recruiter and I would like to request the IT Team to put such options on our company website. However, I might be asked to enumerate several good reasons why we have to put a page intended for the application of candidates. I am planning to create a page that applicants can put on their professional details. What we currently have now is just an email address of HR where applicants send their resumes. I believe that recruiters should not ume candidates have a readily available resume they can just download or send. I hope you guys can give me more reason so I can justify this project. Thanks!