3D printing actually started out as an engineering tool to test products before committing to expensive and hard to change production tooling. The industrial name is “rapid prototyping” and Luma3Dprint also offer this service. The example below shows a geared prototype that was tested in house and adjusted before it went to the production stage, saving many months of sampling time and expense.
These examples show the design stages made in prototype form before the production part was then made. The dimensions of the 3D printed part and production parts are almost identical which allows you to assemble and test a product knowing it will work before tooling starts.