If you are an integrator, you probably need all of them (or at least recent versions) just in case. If you are a machine builder, you can often freeze things once development is built, and keep churning things out. Get everything you need to create great work, plus easy license management, advanced support, and more. If you are an end user, you can often mandate that all equipment on your floor is version X, and use one version.
Each separate install is in the multiple gigs of disk space. This means you may need lots of Portal installs available on your PC, depending on your version requirements. This can be important, because projects can be migrated to a newer version, but they can't be saved backwards: there is no 'Save as V14' option in V15, V14 will not open a v15 project, but V15 can open a V14 one (even if only to migrate to V15). I'll also add to what he said that each of those packages 11/12/13/etc can generally be installed and run in parallel from that same license.
on DVD, license key on USB flash drive, Class A, 5 languages (de,en,fr,es,it). Awesome, thank you JesperMP, making the transition from AB to Siemens and still getting a grasp on the 'new' world SIMATIC S7, STEP 7 V5.6 SP2, Floating License for 1 user, E-SW, SW and docu.
