A few fonts ship with source as well as with the completed TTF or OTF file(s). Unless you intend to modify the font, and have the correct tools (sometimes <xref linkend="fontforge"/>, but often commercial tools), the source will provide no benefit, so do not install it. One or two fonts even ship with Web Open Font Format (WOFF) files - useful if you run a webserver and want to use that font on it, but not useful for desktops.