One more reason for wanting an RPM package is for use within an RPM build system. Typically this uses the mock tool to build the source RPM within a chrooted environment with only the packages declared by BuildRequires stanzas in the specfile available to the build. Without a vendor provided RPM that can be referenced it falls to the end user to create an RPM from the tar distribution so that it can be added to the package set installed by mock for the build.