I’ve started to get spoiled by being able to cut things with my Glowforge that come out the size they’re supposed to be. Yes, there’s kerf, but for one thing it’s fairly predictable, and more importantly for most of the stuff I do it’s well within tolerance even without compensating.
Yesterday I 3D printed something for 8 hours. Not even that big of a something. My Lulzbot Mini is pretty reliable but even then the first attempt failed because the object was so close to the maximum size of the print bed that it happily crashed into an obstruction while trying to reach the far back edge. I kind of prefer the Glowforge saying “no, I won’t go there”, even if it’s currently limiting the print area. But more to the point, after waiting all that time, I now have a lovely augur and a lovely track. And they don’t even pretend to come close to fitting together. It’s not a matter of filing down the edges, it ain’t gonna happen. So I get to play around with the settings and try again (sometimes deliberate underextrusion helps), or hope I can scale one piece up and the other piece down without causing any other problems, or my go-to-last-resort step of importing the model and trying to tweak it in CAD (not so easy with STLs). I’m going to wait until my order of ball bearings arrives, because there’s a very good chance that the holes are too small for the marbles and I might as well not burn another 8 hours to find that out.
By contrast, I wanted to mount some control knobs in a sheet of acrylic. I measured them with my calipers, typed in the number, hit print, and they fit perfectly.