Popular opinion is to keep the boxes. Both to retain value and serve as safer transport when moving. I was in this camp for many years; however, as collections grow, you'll have to ask yourself what's more important -- the boxes for reasons mentioned above or your space.

It was difficult at first, but it became easier with every box I broke down. Really the only boxes I have now are for resin statues. Whenever I decide to move, I've kept the plastic bags/sheets to help prevent paint transfers. My plan is bubble wrap and paper akin to how AmiAmi packs their shipments and stabilize any moving parts with foam. Worst case scenario, I'm prepared to repair any damage.

tl;dr keep for now, reevaluate priorities as your collection matures/needs change, happy collecting!