Used bubblewrap meaning all the bubbles are popped. 

Small compromise, if they stored nicely then keep it (eg: stacked into a perfect rectangle, cut and rolled into cylinder of equal size)

Hoarding. As someone who just cleared out my sister's basement, it is hoarding. Especially when you have empty plastic bins that aren't being used but all the cardboard is starting to get moldy

Every time I get rid of them i almost immediately need to ship something and wish i had them. I keep them not because i need them but because I'll need them if they aren't there

Estimate how much floor space they are using, and estimate how much time and money they would cost to buy new ones if needed, and ask yourself if spending that amount of time and money to get that floor space back would be worth it.

packaging science go brrr