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.
It definitely can have a big impact, especially if the old nozzle wasn't quite flat or smooth at the tip. Or if it was just worn out from lots of use.