Speed and reliability. Take open source. You could manually find, download, untar, configure, make, install and track dependencies. A good package manager lets

Speed and reliability. Take open source. You could manually find, download, untar, configure, make, install and track dependencies. A good package manager lets you do that in one command e.g.: $ brew install package_name OSX includes a package manager for proprietary packages blessed by Apple. It's fast and reliable but its curators forbid most open source and proprietary packages. It's called App Store.