The concept goes way back. On wooden ships,ship carpenters made things, and did repairs from planks of wood. Modern ships carry machine shops. It makes even more sense in space — given the cost of lifting spare parts to orbit.
Remember, you have to pay the cost of lifting the filament for the 3D printer to orbit. The big saving is that only parts actually needed would have to be printed. No need to have spares of everything "just in case."
The cost of lifting the spare parts is essentially identical to the cost of lifting the raw materials to make those parts.
What this does is possibly allow for a smaller number of spare parts to be sent up, using the raw materials to make those parts that turn out to be needed.