0.6 mm is the right default for large functional work. 0.8 mm is right when the part is genuinely big and nobody will inspect its surface.
Why 0.6 mm is the usual answer
It roughly halves print time against 0.4 mm — a 60 mm cube drops from 3.95 hours to 1.93 — while remaining compatible with almost every published profile after a modest re-tune.
Its 0.68 mm lines mean fewer perimeters for a given wall thickness, and its 15 to 40 mm³/s band is comfortably inside what a modern hotend can supply. Detail loss is real but modest: text and features below about a millimetre stop resolving.
When 0.8 mm earns its place
For parts measured in hundreds of millimetres. Its 0.9 mm lines and 0.6 mm usable layer height put down plastic four times faster than a 0.4 mm nozzle, and the reference notes something people find counter-intuitive: the thicker, fewer welds usually make the part stronger rather than weaker.
The costs are unmistakable layer lines, no small holes or threads, and a part that looks like what it is. For a vase, a planter, a mould former or a structural bracket, none of that matters.
Where the ceiling really is
At 1.0 mm the nozzle stops being the limiting factor. Its 25 to 70 mm³/s band exceeds what most stock hotends can melt, so the machine flow-limits and the extra diameter buys nothing.
If you are considering a nozzle above 0.8 mm, the question to answer first is what your hotend can actually deliver. A high-flow melt zone is the prerequisite; the nozzle is the easy part.
The setting people forget to change
Layer height. Fitting a 0.6 mm nozzle and continuing to print 0.2 mm layers throws away most of the benefit, because line width is only one of the two terms in flow.
Match the layer height to the nozzle — up to about four fifths of its diameter — or the swap was pointless.
A practical compromise
Keep 0.4 mm as the calibrated baseline and treat a larger nozzle as a per-job choice. Big parts, filled filaments and anything overnight go through the bigger one; everything else stays on the profile you already trust.
See the trade in the 0.6 mm and 0.8 mm nozzle references, or model the difference in the print time estimator.