Printing is the fastest way to hold your design in your hand, and the easiest way to draw the wrong conclusion from it. A printed part has different mechanical properties, different anisotropy and different surface behaviour from the production part, so the useful question is never whether to print but which question the print is being asked to settle.
Fit questions
For clearance, envelope, ergonomics and assembly order, almost any process works and the cheapest one is the right one. Filament printing in a common polymer answers these for very little money and within a day. Do not pay for a fine surface or an engineering material to check whether two parts collide.
Function questions
Snap fits, living hinges, clips and load bearing features need a material that actually behaves, which in practice means laser sintered nylon or a machined part. Filament parts are weak between layers and will break along a plane that the production part has no reason to fail on, which produces false negatives that send designs backwards.
Appearance questions
Resin printing gives fine detail and smooth surfaces, and finishing gets it the rest of the way. This is where the price of a prototype is genuinely justified, because appearance is the one thing a screen cannot settle and because a finished appearance model is what unlocks a decision from people who do not read drawings.
What printing never proves
Whether the part can be moulded. A printed part happily has zero draft, sharp internal corners, wildly varying wall thickness and undercuts everywhere, and none of that is manufacturable. If the production route is moulding, run a manufacturability review against that route in parallel, rather than discovering it when the tool is quoted.
Questions people ask about 3d prototyping
Which printing process is best for prototypes?
Whichever answers the current question most cheaply. Filament for fit, sintered nylon for function, resin for appearance, metal for anything that has to behave like metal.
Are printed prototypes strong enough to test?
Depends on the process. Sintered nylon parts are genuinely usable mechanical parts. Filament parts are weak between layers and will mislead you on failure mode.
How fast can I get a printed prototype?
Often within a day or two, and same day in some metros. That speed is the main reason to print at all, so use it to iterate rather than to get one perfect part.
Should the prototype be printed in the production material?
Only once the geometry is settled, and only if the printing process can use it. Otherwise test shape cheaply and confirm behaviour separately.