You can't always fit all the storage you want or need into your PC chassis, and sometimes you don't even want to. If you for example want to connect an old hard disk to access files you can't find on the new hard drive after having reinstalled the OS, then it's actually better not to.
Added to that are memory cards of various sizes and capacities. Scythe has come up with solutions for all types of scenarios. There is the Kama Dock (about £24) to which you can connect 2.5-inch and 3.5-inch hard disk. This is an external solution, in other words. Scythe also has 3.5 and 5.25-inch modules that you can install, such as the Kama Rack 3.5 (about £16) and the Kama Rack 5 (about £20). Hardware.Info reviewed all three products.