Use 3D printing to vary the density of production plastic parts.
Most 3D printed parts have the option of varying their percentage of infill. Infill is the honeycomb-like patter inside of an FDM printed part which helps to reduce material used while still creating a structurally sound part. But this infill has another advantage. It allows a part to be created with basically any weight needed (up to the solid density of material) without changing its dimensions. This means that 3D printed parts can emulate the density of other materials like various types of wood.
We recently had a project where this was a great resource. Our client had a prototype of several pieces of their product. The pieces were created to interact with each other in a particular way based on weight. Their prototypes had met their needs, but they were made out of wood. Going into production with any process the client needed a means to match the weight of the wooden prototypes. This was only possible with 3D printing.
Slant 3D was able to create a part with the same overal dimensions of the wooden prototype and then vary the infill density until the production part weighed exactly the same as the wooden piece. This isn't possible with injection molding. The client was elated.
The control of density that 3D printing allows is an incredible advantage of the technology. It allows the possibility of created pieces with the density varying throughout to create parts like self-righting chess pieces. Or one can create parts with high or low densities that they sink or float with the same volume. Nothing else can do that.