One reason to put it outhere...

I have multiple reasons but here are a few...
Don't you hate it when you lose saved projects after reinstalling an OS ?

Well, it happened to me twice on my life-time, when CD's were "the next best thing" for storage digital resources or any data for that matter

Sharing is nice. In my line of work I do have to deal with "hey dude... do you have this thing editable...?"

Review & Inspiration. Sometimes is good to go back to an older project and review it, make it better or apply a new style to it.
"Lol, I don't have this photoshop style anymore... I can take it from this work..."

So yes, having a "backup" its not a bad idea