Why would an ASP.NET page be empty, but for a user control (.ascx)?

I was hired to do some maintenance to a web site, and I found that there is a user control (.ascx) for every page (.aspx) and only one, like a one-to-one, and every .aspx is empty except for the user control. I dont see the use of that, because every user control is the entire page. Is there a benefit for doing that, or is it useless? I'm afraid to say is something useless becouse I dont have much experience.