The very real downside is that your kids become attached to their creations. So you end up with a house perpetually full of cardboard and fighting a constant battle to part with some of it.
I strive to be open and honest in my parenting, but these battles just don’t seem worth everyone’s investment. A box spaceship that hasn’t been touched in a week is quietly “disappeared” to the basement, and if it’s not inquired after by the end of a month it goes to recycling.
Instead, you need to complete the lifecycle of a creation. They should know things they make won’t last forever, and you need to encourage the destruction when the time comes, and after that, they can create a new thing to fill the void, and the cycle continues.
My mother, OTOH, while not the greatest in the world, would ask me to choose which toys were being donated to "other children who don't have any" (Goodwill, probably). I keep things longer than I should, but can throw away the unused from time to time, keeping my house sort of tidy-esque, kinda.
When I was in my early teens, I walked in on my mom going through my brother's toys with a bag in hand to get rid of them. Once I figured out what she was doing, I asked the obvious question, if she'd ever done it to me, and she just nonchalantly asked me if I had ever missed any toys.
I never had. She actually knew which ones mattered and which ones didn't. These days I miss the magic fairy that comes in and gets rid of the things I don't use anymore when I'm not looking!
No comrade. Is better if box spaceship falls from balcony or attends special tea-party.