Here’s why Winrar, a program built to use the RAR format supported by dozens of operating systems, is needed: Winrar, a program that is needed to open and use compressed files downloaded from the Internet as well as compressing and storing existing files, makes the user’s job easier with many benefits. In order to use or open these files, the file compression program Winrar must be installed on the computer. Today, many files downloaded from the Internet appear as compressed files.