I'll chime in so that blueheron isn't all lonesome on the "I cut some ahead of time" side!
I cut two sheets in half for card bases...one for each orientation...and score and fold them. If they are light colors, I might do more. In reality I usually use white card bases so these cut bases might last me a while.
Then I cut a couple of sheets into quarters. These get used for any of the odd sized layers I might be making.
Now, if I decide to make a card bigger than A2, then I just get a whole sheet from my supply.
All the cut paper, card bases, and scraps are then stored in my sterilite drawers by color groups. Bulk paper storage is below my desk.
I've attached a couple of pics for visual learners