My company ordered a 0.4mm ObXidian nozzle for our Prusa Mk4 printer. We ordered it because someone wanted to print something with abrasive carbon-fiber-reinforced filament.
It's mounted now and It's the same diameter as the stock nozzle we've been using so far. Since I had to run a print and the bgcode file was made for 0.4mm, I just ran the print with plain old PLA.
And... wow! The difference in quality is staggering. Particularly on vertical walls: they're so smooth and shiny, it's incredible. And the top surfaces are so much nicer and smoother than with the regular nozzle. I printed that particular print several times before and while it wasn't bad, it's never been that good.
I didn't realize the nozzle impacted the quality of the print that much.
I have yet to use anything other than the stock nozzles as I haven't ran into any printing issues yet that would justify it, but I've heard many people say a high quality nozzle makes a world of difference. Even if they're the same size, I wonder what about the better nozzle improves quality? More uniform heat or something?