Went looking for some cardboard for use in my raised beds in the backyard. Found a bunch in a dumpster behind a dollar tree. Cardboard can also be used as fuel for a fire (just make sure to remove the plastic tape!).
I congratulate you for finding a reuse option for the cardboard. My use for cardboard and paper has been a dual purpose mulch/weed barrier. I like to lay the cardboard on the ground leaving holes only for desired plant. I then cover with woodchips or straw. This combination blocks out the vast majority of weeds but lets rainwater pass right through. Further, the cardboard/woodchip/straw combination really shaded the soil and prevents the soil from drying out in summer heat.
Just my 2 cents, but you what you think is best for your circumstances.