For most people that space is taken up by caching other peoples work, AKA movies, programs, music etc. After I could stream HD content over my internet connection I feel little need to keep a local copy of most of these so I have actually started to use less HDD over the two years.
It's still feels odd, I filled up a 750GB HDD then I got a 240 GB SSD and a 2TB HDD and yet I find I am useing less HDD now than before the upgrade.
It's still feels odd, I filled up a 750GB HDD then I got a 240 GB SSD and a 2TB HDD and yet I find I am useing less HDD now than before the upgrade.