3d printing is excellent at producing small batches of specialised parts cheaper than using injection moulding or making the components out of metal - or even hand crafting. Designs can be send directly from CAD to our print farm and partcs can be manufactured immediately allowing for rapid design iteration and turnaround for urgent jobs.
sometimes you just want something to help you make something else, where its clamping, holding, gripping, guiding or drilling, 3d printing can rapidly produce custom jigs ro help you make that tricky part.
you may not have yet decided exactly what it is you want to build. 3d printing helps you (or you client) to experiment cheaply and rapildy until you reach that perfect design...
finally if you are a little business (most of us are) you dont want to have to order 100’s of parts from a supplier when all you need is one. 3d printing helps you make what you want, when you want with no overstocking or waste.