Somewhere between useless and a godsend. It depends upon your application. There are many choices in materials and printer set-up options that greatly change

Somewhere between useless and a godsend. It depends upon your application. There are many choices in materials and printer set-up options that greatly change the results that you get. Depending on how demanding your application is, you may or may not find the result meets your needs. A friend that is a freelance mechanical designer for medical devices has a small, inexpensive (relatively) SLA printer, and she sometimes is running it flat-out for days doing prototypes to show clients. Instead of sending that to a service and billing it through, she gets to bill it directly, allowing for a nice margin and also giving client a discount. My friends that build hobby robots use FDM printers for a lot of functional parts -- and results vary depending mostly on how appropriately the part was designed. But a Prusa is a lot cheaper and a lot easier to run than a CNC milling machine, on the flip side a chunk of FDM plastic doesn't compete well with a chunk of aluminum or titanium. At my work, we 3D print a lot of functional enclosures and other low-mechanical-load parts for prototyping.