I built a four-poster bed, and 3D printed the fittings for the curtain rails and the attachment point for the fan.
I built a desk, and 3D printed the entire shelving system for it.
I designed and 3D printed an entire range of boardgaming accessories (storage bins, dice towers, meeples, etc)
I only bought the thing as something to do while in COVID lockdown. But it's been really useful.