Oh really dear dear dear !!!
I think ONE reason assuming you are using Windows and no NAS boxes etc is that with huge multi-media files etc is that even with largish HDD's you might find your multi-media libraries can easily outgrow the size of typical HDD's.
Since W8 the concept of Storage spaces has been added which allow you to aggregate Physical volumes -- which unlike RAID --- can be of DIFFERENT capacities!!!! -- into logical Data storage pools / spaces and you can dynamically add more volumes when you need. You can also use mirroring / striping as Software RAID also without the need of physical volumes having to be the same size.
While W7 can READ these data spaces it can't create them or have them on its own machine. You have to share files from W8 and higher computers.
I've found this a really useful feature - and a good use for older HDD's that have been replaced with larger capacity ones -- I'm using 4 X 750 GB HDD's as an approx. 3 TB storage space.
(Linux users can consider Windows storage spaces as LVM in their distros -- approx. similar. Incidentally using Storage spaces for RAID - especially as you can have different sized volumes in the mix works very well indeed - you won't need on a home computer a RAID hardware controller any more.).