Multi-material printing is one of those features that looks magical in the marketing render and rather different on the bench at midnight when the printer is wiping its third colour change into a tower of waste taller than the part itself. I've now done enough of it to have an opinion, and the opinion is: occasionally brilliant, mostly not worth it.
Let me be specific about the cost, because that is where the romance dies. On a single-extruder system doing colour changes, every transition means purging the old filament out of the hot end before the new one is clean. That purged plastic goes into a "wipe tower" or a prime blob, and it adds up fast. A two-colour print can easily burn more material into the tower than into the model. The print time roughly doubles, sometimes worse, because the head spends its life travelling to the tower and back rather than making your part.
So when does it earn its place? Three honest cases, from my own bench.
- Dissolvable supports. This is the real one. Printing PLA with a PVA support interface, then dropping the whole thing in water and watching the supports vanish, gives you overhangs and internal geometry that are genuinely painful any other way. The waste hurts less because the support material was always going to be thrown away.
- Embedded text or logos that you want in a contrasting colour and don't want to paint. A label moulded into the part survives wear in a way a painted one doesn't.
- Functional plus flexible, like a rigid PETG body with a TPU gasket printed in place. When it works it saves an assembly step entirely.
Everything else, the two-tone desk toys and the rainbow benchies, is mostly for the joy of it, and there's nothing wrong with that. I'm not above printing something pointless and pretty. But I've stopped pretending it's efficient.
The honest summary: multi-material is a capability, not an upgrade. If your problem is "I need a support material that comes off cleanly" or "this needs two materials in one go to function," it's transformative. If your problem is "wouldn't it be nice in two colours," budget for the waste, the doubled time, and the failed change that ruins hour six of a print. Sometimes nice isn't worth it. Sometimes it absolutely is, and you'll know which is which by the second spool.