Because for USB flash drives, hard drives you can store thousands of data on them, music, videos, photos, software, tons of documents etc.
For Blank Discs I use them allot to burn photos, docs, music, audio books, eBooks.
I love to collect photos of everything nature, animals, horror, cartoons, photography is my passion
Anyway whole reason why I love to burn data onto blank discs is you never know if a hard drive or USB flash drives goes corrupt always have a good back up copy.
For burning data I use allot of DVD-R or DVD-RW since most sites are closing down these days, Google always refreshes it's pictures from years like for example I could not find that photo I wanted in 2008 so I started to collect photos then burn them to my blank discs for safe keeping, It's like having your own offline website or offline directory of data
You just put the disc in the optical drive it opens up with out internet if a person does not have net for example. The best part is drag and drop it onto your desktop.
It really feels like a person tapped into a computer or network and is taking the files from some one but there not When they were the ones who burned the disc lol.
The feeling of copying the data from a disc is like having your own personal data that no one in the world as at the moment, that's the feeling or like you just committed intrusion and then no one knew about but they never have lol.
For me I always burn documents I have thousands and thousands so far I also have tons of World Music around maybe 5 thousand albums so far kept as back up copies.
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If you use a hard drive much the same way as a optical disc (as in only plugging it in to copy stuff to and from it) it should last just as long as any disc.
Yes a HD is prone to mechanical failure but a cd is also prone to being scratched which can lead to it being unreadable.
As long as you don't go wiping a high powered magnet over the HD it will be perfectly fine.
Just out of curiosity i just plugged in an 80gig HD that i got out of my cupboard and is god knows how old and it booted up perfectly fine, everything was readable.